You are doing good...How did the offer on the house go? I hope it went well.
I see you are doing well with your boundaries, but I am concerned about the involvement of drugs and the possibility that your son may be in drug environment. If you think your wife is using and has shown signs of losing a lot of weight, I would gather that we aren't talking baby drugs either. I would suggest finding out if the guy is really dealing drugs and if so you may need to enforce a boundary. Children need to be protected and that is the parents responsibility. Your wife is looking out for only herself, so you know what has to be done if the situation is what you think.
Your friends-They are reminders too your wife of the life she is giving up...don't expect her to talk to them any time soon.
OM-Carefree and independent...not answerable to anybody. Don't worry about him other than exposing your son to a drug environment. The reality being that he will soon bore of your GF and move on to the next piece. She thinks he is the answer, but he is just a distraction from her own pain.
Listen to Amy...she will offer you invaluable insight into your wife's mind. Jack and Mach aren't too bad either.