Remember this small quote If nothing changes nothing changes!!!
Ive taken mine back 2 times now, and its worse every time they try to make you feel like its your fault and that you owe it to them to help them, once you let them back its 10 times harder to make them leave because you broke your boundries then they think they can continue to break you down, believe me sister I am there, just say a prayer, hold your head high and if he is truely serious about recovery give him 6mos to 1 year to get it together, Im a recovering addict of 7 yrs, its better that we dont have someone to lean on, we like people to enable us, it makes our using easier. That way we dont have any real responsiblities, It took me to have nothing and no one to finally come to terms with what I was doing to finally get it, recovery..
Its hard work alot of steps and a great sponsor the rest comes after that, sometimes i still make weak choices one being in the situation I am in now with my addict bf, your right when you said your MIL dosent have to live with him, they never want to know thier precious sons are annoying and out of control.. My prayers are with you think long and hard before you let him come home...