It's bad to cheat on someone.
Trevor is in a relationship when he meets a new girl he thinks he really likes.
Trevor wants to sleep with the new girl he met.
Trevor takes the time to end his current relationship before sleeping with the new girl he met.
Trevor sleeps with the new girl he met behind his current partner's back.
Trevor ends up in a long term relationship with the new girl and is very happy with her.
His partner finds out about his cheating and it ends up ruining his relationships with both his partner and the new girl he met.