When Sean re-enrolled at Degrassi, Peter felt that his relationship with Emma was strong enough to withstand Sean's re-entry into Emma's life. In fact, Peter was eager to befriend him. Sean hung out with him a few times and helped him fix up his new car, but behind Peter's back, Emma cheated on Peter with him. When Emma was not around, Sean blew off Peter, and Peter quickly figured out that Sean was after his girlfriend when Emma went on break with Peter. Peter, who was furious, got Sean suspended indefinitely from school by framing him when he put marijuana in Sean's locker and told his mother, Principal Hatzilakos, as a "tip" that Sean had drugs. Sean challenged Peter to a street race, and ended up hitting a local pedestrian. He ran from the scene before the police showed up, and was charged in jail for his hit-and-run offense. Emma later figured out that Peter framed Sean, and broke up with him. After Sean got out of jail, he and Emma began another relationship.
Season 6In Here Comes Your Man (1), Sean and Peter meet for the first time when Emma introduces them. At this time, Sean is back at Degrassi and Peter is Emma's boyfriend. On the first day of the new school year, Sean watches Emma and Peter kiss in the parking lot. Later, Sean helps Peter fix up his car, and tells Peter to meet up with him where at the street races. Emma is not keen on the idea, but they head to the races anyway. Jay Hogart is confused at why Peter and "his dad's car" is at the races and waving at Sean, but Sean tells them that he is going to mod his car. Alex comments that Sean is "Keeping his friends close and his enemies closer", implying Sean is using Peter to get to Emma. Sean promises to help Peter modify his car, and leaves Peter with Jay to go to talk to Emma. Emma and Sean are attracted to one another still, but Emma pulls away from him because of Peter. She tries to avoid seeing Sean, but gives in when Peter wants to go hang out with him. Jay and Peter have an illegal street race, and when the cops come to break it up, Emma escapes with Sean in his car. She then cheats on Peter with Sean while ignoring a call from Peter.
In Here Comes Your Man (2), Emma feels guilty for cheating on Peter, and leaves Sean in the car when he drops her off at home. Peter asks her if Sean is coming inside and wants to hear what he thought about the race, oblivious to the fact that his girlfriend cheated on him. The next day at school, Peter shows up at school dressed exactly like Sean. He greets Sean and asks him if he is down for another race that night. Sean asks if Emma doesn't mind being dragged to the races again, but Peter said it would only be him and Sean. However, Sean blows him off because he says that he has calculus homework. Peter offers to help him with it, but Sean rejects his offer. Sean keeps trying to win Emma over, but he only makes her feel more confused.
Emma decides to go on break with Peter, and Peter figures out it was because of Sean. He says that he feels stupid for ever trusting him, and Emma tells him that it wasn't Sean's fault that anything happened. Peter asks if they had sex, and Emma says that she isn't a slut, to which Peter says, "Could have fooled me." Peter, who was angry at losing Emma, frames Sean by putting marijuana in his locker, and gets him suspended indefinitely. When leaving the school, Sean asks who would do that to him, and asks Emma if she told Peter about them. Sean claims that Peter did it, but Emma doesn't believe him, instead believing the drugs were actually Sean's instead. Emma later makes up with Peter, who denies any ties to the drugs, and lies to Emma, saying that he knew Sean was into some drugs. Peter tells Emma that Sean was his friend and he would never do that, saying the tip to his mother most likely came from a drug connection.Sean, who is furious, tells Jay that he is going back to Wasaga Beach since Peter has already won, as Emma believes he is a drug dealer and his mother would have him arrested if he beats him up. Jay gives him the idea to challenge Peter to a street race as revenge. Later at the races, Sean approaches Peter's car, and Peter asks what this is about. Peter says that Sean tried to steal his girlfriend and asks if he was never taught about the guy code. Sean talks about asking Peter if anyone taught him about fighting his own battles, not getting his mother to do it for him. Peter provokes Sean by admitting in his mom's office they keep locker combinations, which Sean figures out that Peter used to get into his locker. Peter accepts Sean's offer to race, but during the race, Sean hits a jogger. This stops the race, and Sean calls for an ambulance. Jay shows up and convinces Sean to run since he is 18 and would be put in hail, even though he would be committing a hit-and-run offense. Sean flees the scene, while Peter and Jay stay behind. He runs to Emma's house, who tells Sean that he needs to turn himself in. Emma tells Sean that she can't care about him, not anymore.
In True Colours, Peter tells Emma that he basically got off with the judge with just community service and house arrest, while Sean will go to jail. Emma tells Peter that she now has a no tolerance policy when talking about Sean. Jay comes to school to talk to Emma about Sean, and asks if she'll go to his court hearing the next day since he can't make it. He tells Emma that Sean will get beat up in jail, and that it isn't fair that Peter got off with such minor punishment. Emma attends Sean's court hearing, which ends quickly because Sean's lawyer didn't show up. Emma asks what she can do to help, and Sean asks her if she is still with Peter, to which Emma says yes. Sean calls him slime and says that Sean planted the drugs in his locker, though Emma still doesn't believe that Peter did it. When Peter leaves a mask in her locker for the dance, Emma later makes the connection that Peter did plant the drugs in Sean's locker after talking to Manny Santos. Emma confronts Peter in the hallway, and asks Peter if he planted the pot in Sean's locker. Peter says that Sean will always be a loser, but Peter admits he did it, but to keep Emma and him together. Emma breaks up with him in the hallway, and heads to see Sean in jail.
In Crazy Little Thing Called Love, Peter overhears Sean arguing with Emma and laughs at her.
- Peter: "It's just a little fun. What do you have against that?"
Emma: "Nothing. I'm all about fun. In fact, if fun were people, I would be China."
Sean: (smiles) "Okay..." - Here Comes Your Man (1)
- Sean was eleven months older than Peter: Sean was born in October 1988 while Peter was born in September 1989.
- They both dated Emma Nelson.
- They were both friends with Spinner Mason, who later married Emma.
- They were both considered to be troublemakers.
- Both were emancipated at some point in the series.
- Peter had a conflict with Sean's friend, Manny Santos.
- They both attended J.T. Yorke's funeral in The Bitterest Pill.