Sister, I'd change the locks. The responsible thing for me to say is get legal advice first.
But if you really feel as you say, you want him to just go, kick him out and initiate proceedings. If he gets clean later, you can figure out how you feel then.
No one should have to live the way you are living now. I'd create a little distance from MIL, too.
I hate the situation that drug addiction creates for all of us.