Why do Wives cheat?

My Stepmom is cheating on my Dad and what angers me the most is she gave him all these reasons why she wants a divorce a couple aweeks ago only to find out the real reason just yesterday is because she is cheating. Whom I believe she's been seeing off and on for 7 yrs. now but she stayed with my dad long enough (12) for his pension, alimony, child support, and the list is endless. He put a recorder in her car and caught the w**ore lieing and cheating! Her kids well 2 of them are rotten and make mean remarks/ geisures about my dad and expects they must expect me to sit back and not say nothing. The oldest daughter called my dad 3 days ago and threated him that he better watch his back. I need help on what to do? Also, is commiting adultery in the state of OHIO still against the law and is grounds for No alimony and so forth?