Welcome to SoberRecovery!
This forum has taught me so much and I truly do not know where my children and I would be without the lessons that I've learned from the people here.
Please take time to read the stickies at the top and to read other posts that share experience, strength, and hope.
I am the mother of a 13-year-old son. I am currently separated from my AH. My AH and I have two younger children together, ages 4 & 3. So far, my 13-year-old has suffered the most from his step-father's actions. It's hard to be a young teen. Those years are difficult for any child, even children in perfectly functioning homes. It has to be so much more difficult for children with addict parents. It's good that he's in counseling. Are you two able to possibly go to family counseling (just you and your son)?
Do you feel like your son is generally happier now that he is not in the same home as his father? Do you believe his father is still using oxy or any other drug? It is exceptionally hard to break away from the grips of oxycontin. If you suspect dad is using, why is your son spending half of his time with him?
Please, if you take anything away, let it be this: DON'T FEEL GUILTY! You absolutely did the right thing by moving you and your child out of the home of an addict. You did not tear your family apart! Addiction did. Recovery is in your AH's reach, but he has to make that choice. I don't personally know you or your son but I find it very difficult to believe that your son's pain will go away if you reconcile with your AH. Further, if AH is still active in his addiction, it will put your son in danger (again).
You did not cause, nor are the cause of, your husband's addiction
You can not control your husband's addiction
You can not cure your husband's addiction
I can relate. I've threatened my AH with the police for writing checks off of my account. I went to our local grocery store to demand they not accept any checks from my account until they verified it was me writing them. (He'd buy something for a couple of dollars and then write the check for $80 more) I also had to go to my bank and alert them to what he was doing. It's so embarassing.....and sad. It sucks that you or I even had to deal with an issue like this from a person we believed would love us more than anyone.
I'd also advise you to check out the books, Codependent No More and Boundaries.
((((HUGS)))) to you!