Have you thought about calling a local woman's shelter and talking to a representative there?

Mental abuse is worse than physical abuse because it leaves no track. Even if you love your inlaws, you need to talk to someone who could help you get out of the situation. Also, if you are going to leave, do NOT tell him. Do it when he is working etc., to prevent him from convincing you to stay.

Abuse is a nasty cycle. He will continue to manipulate your emotions and break you as long as you stay.