People shouldn't have sex with other people's partners.
Robert is single and often hangs out with a nice couple, whom he knows are going through a rough patch in their relationship.
Robert wants to have sex with someone soon.
Robert keeps on looking for a partner and meets a cool girl with whom he sleeps.
Robert has a tryst with the wife of the nice couple.
Robert's relationship with the new girl is wonderful and Robert is over the moon.
The couple ends up divorcing because of that and Robert feels really guilty.