You shouldn't sleep with someone's partner.
Adam is out with his friend Thomas and his wife JIll for dinner and Adam is attracted to Jill.
Adam wants to spend more time with Jill.
Adam tells Thomas and Jill he enjoys hanging out with them as friends.
Adam calls Jill later that week and sleeps with her in her house.
Thomas and Jill feel flattered and hang out with Adam more often.
Thomas finds out about it and gets a divorce and ends his friendship with Adam.