Welcome Papillion.
I know it must be painful to watch your son struggling with all the changes happening. When parents separate it is often hard on the kids, regardless of addiction issues... Its wonderful that he is in counseling and enjoys attending the sessions. This is going to benefit him so much in the long run. Possibly, some of the distance between you may just be caused by his age right now – preteen? I know it is tempting to think if the family all got back together under the same roof it would maybe help him, but unless there is a change in the actual structures of the relationship with your husband, then I would think it would only end up in an unhappy situation again… for everyone.
If your husband is still in active addiction, then it would appear nothing has changed in the past 12 years. Has your husband talked to his doctor? Had any medical treatment or therapy? Made any positive changes in how he handles life? My husband was also a highly functional user of prescription pain meds. We separated while he was actively using. That time apart was very difficult, but it also allowed me to learn a lot about myself, and grow as a person. Fortunately, my husband did ask for help, went into therapy. I wish I had done it sooner, but at that point I started seeing a therapist also. It was very helpful to me in dealing with my feelings, events of the past, learning about addiction, and defining what I wanted for my life. So I always suggest this to others. In the stickys at the top of the forum there are some links to sites like National Institute of Drug Abuse, the Addiction series by HBO. These sites also have a lot of information related to prevention of drug abuse in regards to children. Due to my husbands past issues, I find myself soaking up all this info.
Very sorry your situation brought you to SR, but there is a lot of information here & I hope you find it a source of support and encouragement. (There is also a forum here for parenting /addiction issues).