The relationship between Carter and Serena, also known as Carena, is the relationship between Carter Baizen and Serena Van Der Woodsen . They began dating in the start of Season 3 .
Blair hosts a party for CeCe at her penthouse in Hi, Society and Carter attends. This is the first time Dan meets Carter. CeCe tries to show Serena that Carter is a good choice for a guy, a "phoenix risen from the ashes", but Serena does her best to ignore her since she was there with Dan. CeCe tells Dan that girls like Serena end up with the Carter's of the world and not the Dan's from Brooklyn. She goes to see Rufus at his art gallery and offers to buy Alison's artwork in return for his making sure Dan does not go to Cotillion with Serena. Rufus tells Dan and when Dan tells Serena, she does not believe him and they decide not to go together. CeCe calls Carter and he escorts Serena instead. Meanwhile, Chuck is still mad at Carter and manipulates Nate into thinking he is interested in Blair. Nate punches Carter in the middle of a dance and he is not seen again with Serena until season two.
Carter begins dating Blair, much to the dismay of Chuck and Serena. To get him to leave, Serena blackmails him with their time in Santorini together, and along with Chuck, they successfully drive Carter out of the city with a one way ticket to Dubai. Serena runs into Carter in The Goodbye Gossip Girl and he tells her that he found her father in Fiji and they once again take off together to find Dr. Van Der Woodsen.
Serena returns to New York in Reversals of Fortune and is still being harassed by the paparazzi due to her arrest. Jenny and Eric have been hiding Serena's exploits from Rufus and Dan, but when they find out, they recognize Carter in almost all the pictures but don't know who he is. Carter meets Serena outside her apartment building and says they need to talk and that Serena can't avoid what happened forever. She unties her halter top dress to get away from him and leaves. Dan asks Serena who he is and she says that they traveled together at the beginning of summer but then things got weird and Carter is stalking her and she doesn't know what to do. She asks Dan to keep him away from her at all costs, and Dan calls Blair for help. At the polo match, Blair and Dan confront Carter with a restraining order against Blair, since she will be by Serena's side at all times. They call Serena over, who once again claims Carter is stalking her. Carter says mysteriously that that isn't the truth at all. Serena throws the first ball at the match and takes off into the woods and Carter follows. He meets up with her and he reveals that the truth is that her father didn't want to see her. Serena becomes upset and Carter tells her he would have stayed around for her all summer but she ditched him and ran. The two kiss and have sex in the woods. However, Serena once again runs away and leaves a shirtless Carter with the stolen horses from the polo match.
In The Freshmen, Chuck tells Rufus that Serena is hiding out at the Palace and is not going to Brown. As revenge, Serena calls Carter and asks him to go out with her later that night. At the bar they're at, Carter sees Chuck having a meeting and wants to leave. Serena tells him crashing would be fun so they go over to the meeting and successfully ruin Chuck's deal. Carter realizes the only reason Serena asked him out was to embarrass Chuck and gets angry because he told Serena how he felt and she blew him off. He tells her to find a new bad habit since he isn't willing to be hers anymore. At the end of the episode, Serena finds Carter and apologizes to him, saying that he is not her bad habit, that she always comes back because he is always there for her and she trusts him. She tells Carter that she wants him and no one else. The two kiss and make up.
Serena and Carter are officially dating in The Lost Boy. Serena tells Dan that she is happy with Carter and that she is pleasantly surprised with him as a boyfriend. Carter invites Serena to his hotel room at The Downing and is interrupted by a girl named Aubrey who claims to have slept with Carter and he doesn't recognize her. Serena is confused and leaves. Blair tells Serena that Carter really isn't the good guy she thinks he is and that guys like Carter don't change. When Carter tries to check out of The Downing, his card is repeatedly declined and the concierge is being instructed to destroy the card and call the police. When he looks at the bill, he declares he didn't order any of the room service he is being charged for, including three bottles of Dom 95 Preserve. Serena tells him he can use her card and that he should at least pay for room service and Carter again denies ordering any of it. Serena is visibly skeptical and Carter is disappointed that she didn't believe him about the girl from earlier or the room service bill. Blair and Serena meet up at the Sotheby's auction and Serena admits that Blair was right about Carter and that she shouldn't have trusted him. Blair replies that some guys just are who they are. Chuck remarks a few minutes later that he is surprised Carter isn't there with Serena and that some guys just are who they are, and Serena puts it together. She buys the photo both Chuck and Blair need as revenge for their Carter sabotage. Both Blair and Chuck admit that the girl was a set up, the hotel bill was also a set up (Dom is Blair's favorite champagne), and that they did it because Blair didn't want Serena to get hurt and Chuck hates Carter. Chuck explains that Carter is selfish and when they sent him away, Carter went to Greece instead of Dubai and didn't come back to New York until he was broke. Serena explains that her and Carter went looking for her father in Santorini and she didn't want anyone to know which is why she went to him. They went to crash Dr. Van Der Woodsen's wedding but were on a stolen boat and were picked up by the police. Serena had no idea that Carter was looking for her father by himself. Carter shows up at the Van Der Woodsen's and Serena apologizes for not believing him and Carter says he figured out it was Chuck and Blair the day before. He tells Serena that she will eventually find a reason to bolt if she really wants to, but she says she doesn't want to leave. She invites him to eat breakfast with her family and Carter agrees. Outside the building, Carter runs into Nate's new girlfriend Bree Buckley who tells him that her family will be coming for him after what he did to them.
Carter returns in Rufus Getting Married and is staying with Serena at the Waldorf residence. At brunch, Chuck and Bree briefly discuss Carter and she asks him to tell her if Carter shows up any time soon. Blair tells Chuck she too thinks Carter has changed and that he brings out a new side of Serena. She tells Chuck that he is at her penthouse and Chuck tells her that Serena liking Carter doesn't automatically make him a prince. Chuck shows up at the Waldorf's and informs Carter that Bree has told him everything and he gives Carter the choice to go to Lily and Rufus' wedding, tell Serena the truth and face Bree and her family or leave with a one way ticket he provided. Carter ultimately showed up at the wedding and he tells Serena everything: how he met a shy and kind woman named Beth and he asked her to marry him so that her family would pay off his gambling debts, and how he left her at the altar because he didn't love her. Serena gets upset and walks away. After Lily and Rufus leave the wedding to chase after Scott, Carter asks Serena if she is okay and she asks him to leave because she needs time to think. Carter tells Serena that he really does care about her and he only told her about Beth because it's not the same with her. He runs into Bree with her cousins, Beth's brothers, and he tells them he'll be at The Downing that night because they can't cause a scene at the abandoned wedding. Later at the Humphrey's loft, Chuck tells Serena that he met with Carter before the wedding and that even though he hates Carter, he didn't have to own up to anything and had the opportunity to leave. Chuck explains that Carter risked a lot going to the wedding because of Bree being there with her family. Serena asks if the Buckley's would really hurt Carter and Chuck says they clearly want revenge. She leaves Carter a message saying she's sorry and really wants to talk to him, but it goes to voicemail due to Carter being in a car with Beth's brothers. Nate finds out that Bree had been using him to get to Carter and he tells her to leave.
In Enough About Eve, Nate tells Serena that he heard that the Buckley's are flying him to Galveston so that he can work off his debts on one of the family oil rigs. Serena states that it would take him twenty years or so to work off that kind of debt and Nate says that he thinks they're more interested in getting him out with a bunch of rough Texans. PJ Buckley, Bree's cousin, hosts a poker game with high stakes. Nate thinks they can win Carter from them because Bree told him PJ tells and they will know when to call his bluff. Nate and Serena show up at PJ's and buy into the game with $25,000. However, after a few rounds Serena is losing badly. Nate reassures her PJ is on tilt and this is when they can win. They buy back in and Serena tells PJ she wants to play for Carter. PJ says that Carter's debt is worth a lot more than what Nate and Serena are showing. Nate makes a deal that if PJ will play Carter and he wins, he'll give PJ a photo of Tripp van der Bilt at his bachelor party and PJ agrees. PJ wins, keeps Carter, and gets the photo of Tripp. Later, Serena shows up Tripp's campaign office and offers to explain to William van der Bilt that she is responsible for PJ getting the picture. Nate refuses to let her, saying he can handle it. He takes William's call privately and PJ calls for Nate at the office. An employee comes by looking for Nate and Serena says he'll tell him about the call. She overhears Nate tell his grandfather that he feels bad about lying to Serena and that he has the original picture of Tripp. Outside the office, Serena confronts Nate and takes the picture from him. Nate explains that the photo he gave to PJ was a fake and when they leak it, the van der Bilt's will come out with the real one and prove the Buckley's are villains who faked the photo, and that Carter is hardly innocent. Serena walks away and calls PJ to tell him what the van der Bilt's are planning. Serena waits for Carter in Blair's bedroom and when he shows, she apologizes for what she said to him at the wedding and explains that she settled his debt with the Buckley's by helping them avoid a public fiasco. Carter tells Serena that this was his debt to settle and didn't want to be saved, that he wanted to take responsibility for what he did and needed to prove that to Serena and himself. He tells Serena he would rather her hate him than feel sorry for him and leaves.
In The Unblairable Lightness of Being, Serena is dating Nate. She tells him that she is having breakfast with the Humphrey's but instead goes to meet with Carter. Chuck tells Nate that Carter Baizen is back in town and his friend saw Serena with Carter that morning at the St. Regis Hotel. Nate doesn't believe Chuck until he sees Carter outside Blair's building. Carter tells Nate that he has something Serena wants and that Nate can't give it to her, that he'll be at the St. Regis and that Serena knows that already. Jenny and Eric show up and Nate asks is Serena was at breakfast. Eric lies and says yes and Jenny says no. Nate leaves and Jenny delivers Carter's package to Serena, a hotel room key, and tells her that she got it from Nate who got it from Carter. At Dorota and Vanya's party later that evening, Serena tells Nate that she ran into Carter the other day and told him they could have coffee and anything else he said was to upset Nate. Nate is mad that Serena didn't tell him the truth right away and only did when she got caught. Jenny encourages Nate to look through Serena's purse and they find the hotel room key. The next day, Nate and Serena arrive at Dorota and Vanya's wedding and Nate is still angry at Serena. Serena tells Nate that Carter is helping her find her dad and didn't tell Nate only because she felt stupid and didn't want him to be disappointed in her. Nate tells her he doesn't want her to see Carter again and Serena disagrees, telling Nate he doesn't have the right to tell her who she can't see. During the wedding, Carter texts Serena that he has her dad's exact location which is a three hour plane ride away. Serena is hesitant, but decides to go and make her father see her. She goes to tell someone she is leaving but Carter says they have no time and to call someone from the car. During the reception, Nate asks Jenny if she has seen Serena and she tells him that Serena left with Carter before the ceremony. Once in the car, Serena sees the date on the airplane ticket and figures out Carter was lying to her about when he knew where her dad was. Carter says that he abused the time to see if there was anything still between them. Serena has the driver pull over and kicks Carter out of the car, saying that she won't need his help ever again. This is Carter's last appearance.