Well, kick him out, invite MIL back in.
There is help for him. Salvation Army has a program that really is quite good and is free. Until he leaves, lock up, hide, remove from the house anything of value or it will be gone.
IF he truly wants help, he will find a way to Salvation Army, be it one in Kentucky, Kansas, or Springfield or all the way up in Chicago. If he doesn't, he will just continue using if he is not ready. If he is out of the home, then MIL can move back in and you won't be alone.
J M H O
Love and hugs,