It's wrong to cheat on people.
Jack is married, but a girl he has always had a crush on want to come over to his place.
Jack wants to invite the girl over.
Jack invites the girl over to meet his wife and eat lunch together.
Jack invites the girl over when his wife isn't home, and they have sex.
Jack's wife doesn't have to worry about Jack cheating on her since Jack introduced the girl to her.
Jack's wife could end up finding out and be completely heartbroken.