History doesn’t repeat itself people repeat history. You are living the life his wife did 7 years ago when you first met him.
I am sure she left for her own sake and the sake of her children. He couldn’t stop for his family then he ended up losing them and that didn’t stop him from using again, all he’s done is find someone who is accepting of his habit. You said it’s easier to deal with his drug use then hurt your son or lose his family. Your son deserves far better then this. His family saw how his habit cost him his wife and children how could they not understand you wanting out.
You say there is no connection, no closeness but basically friends with benefits, exactly what benefits are you getting out of this?
The part of you that is saying he needs you is your codependency. Something you may want to research on the internet.
Glad you found this site, keep posting and please put yourself first and your son, not the addict.