Thank you all for your wonderful posts and words of encouragement and advice. I vented to a friend a bit, and then as I worked through it in my head, I decided I need to tell mother in law to butt out. (Which is no easy task since they are Russian, and even though she's been here for 17 years, she barely understands english. I had to have my whole statement translated to Russian online. Sentence by sentence...ugh) I'm not asking her anymore, I'm telling her. He's grown and married. He doesn't need to be mothered. He needs to grow up and be a man. And she needs to give him the chance to learn how to do that. If she respects my request/demand, great. I realize its no guarantee he's going to realize he needs to get help and learn how to stop drinking/using so he can have a decent life, and hopefully we can put our marriage back together. But at least there's a better chance of him coming to that conclusion without her enabling him. If she doesn't, at least I didn't just sit there and let this all happen to me. The heck if I'm waiting until she dies for him to have his "aha" moment.
Anyway, the anger has faded and I feel more at peace knowing I'm going to have a chance to say my peace, and with any luck, effect some change.
Thank you all again, and much luck and support in your personal journeys.