My father-in-law living with us for 3mths now and its driving me up the walls.?

Your husband is supposed to.

If he doesn't do anything, move out and tell him if he doesn't solve the problem, then you'll be filing divorce.

You dont, you ask your husband to do so. Its your husbands responsibility.

Also, you need to address the issues of why he is driving you up the wall.. list them and then have a word with him about how you can "compromise" on these. Perhaps if he eased up on any habits that are driving you crazy, will make it a more harmonious place to stay.

Its always difficult to have a "third" person in your home, you either address the issues, or you and your husband suggest your father in law have a break, and go see one of his other sons, and you feel he is getting "bored" around you.

Tell your husband he needs to this.

Otherwise the father in law could resent you,but his son he will forgive

Insist and demand that your husband tell him he needs to move out permanetly.