Peter McMillan was Bree Van de Kamp's Alcoholics Anonymous sponsor and brief romantic partner.
Peter had sexual and alcohol addiction. Peter managed to beat his alcohol addiction and became a sponsor for AA. Peter is bisexual and has problems with not having sex. Once he can keep a plant alive, and then a pet, then he can have sex again. He is currently on his sixth plant.
Bree Van de Kamp joins AA because her son is suing her and she wants to prove her sobriety. Bree assures Peter that she has been sober for quite a while but she was lying. Bree later gets drunk at a mall and is locked in after closing. Bree gets stuck in between the mall bars while trying to get out. Bree calls Peter who gets the mall security man to let her out. Bree then reveals she might have a "small" alcohol problem. ("Could I Leave You?")
Bree warms up to her AA sponsor Peter who in addition to being an alcoholic is a sex addict. When Bree tries to kiss him, he proceeds to take of his clothes and have sex with Bree on the table. His instincts then force him to stop when he becomes very energetic and rough. The following day, Peter introduces Bree to her new AA sponsor, Donna who is a tough and unfriendly woman who claims not to be a lesbian. Immediately, Bree wants Peter back and tries to win him over. In order to get Peter back, Bree becomes extremely drunk at a bar and passes out. She calls Peter to drive her home who does so against his will and comforts her as he makes coffee. ("Everybody Says Don't")
Peter comforts Bree as her trial between her son is ready to take place. Bree's father Henry Mason postpones the trial. Bree's stepmother, Elanor Mason does not like Peter and thinks he is inappropriate. She tells Henry that "he has long hair". ("Don't Look at Me")
Bree continues to develop her feelings for Peter and attempts to kiss him after an A.A. meeting. However, shortly after, they are caught by Peter's sexual addiction sponsor, Claude. Claude is upset at Peter's bad judgment and tells Peter to say goodbye to Bree. Peter does as he is told and leaves with his sponsor. Bree later visits Claude at the doughnut shop where he works and demand that he lay off Peter. Claude tells Bree that he cannot since Peter will regress and become an addict again. Bree soon receives an idea to bring Peter back. When a cocaine addict visits Claude he hands Claude the cocaine and leaves. Soon after, police arrive to purchase donuts when Bree gives them a tip that Claude is in possession of illegal drugs. Days later, Peter tells Bree that he is shocked that his best sponsor was found with drugs. Bree then asks Peter if he would like her to be his sponsor. Peter rejects the offer since she would not understand. Bree then tries to convince him to accept her since she has experience with men such as Rex and George. Peter later calls Bree from a bathroom at a lifestyle party and asks that she come pick him up. Bree soon arrives where she is whisked into the bathroom and told by Peter that this is what he was once like. Bree tries to assure him that she is caring and will help him to the best of her ability. The two then walk out of the bathroom and leave the party. ("It Wasn't Meant to Happen")
Peter has dinner at Bree's house one night with Andrew, Danielle, and Justin. Bree wants Peter to tell Andrew about the college he attended because Andrew is considering it. Since Bree won't let Danielle have her boyfriend over for dinner, Danielle messes with Peter by wearing a sexy dress and running her hand on his leg. Peter resists his sexual urge by leaving as quickly as he can. Peter goes to Bree's house the following day and Andrew leads him into his mother's bed and Andrew and Peter have sex. Bree walks in on them and kicks Peter out and leaves Andrew on the side of the road the following morning. ("I Know Things Now")