Gerette, I also have a son who is an addict, and who sold. Many do, largely to support their own habit.
I understand your fear of alienating your son entirely, but when he was little, you would not turn your head when he went to play in the street; you took action and never thought twice about it, because you were trying to save his life.
As a minor, he has no say in a treatment "option." Period. I should not be giving advice, but ( ...the big but approaches...) if i were in your situation knowing what I now know, here are some of the things I would do.
Find a treatment program that your insurance covers or that you can afford.
Tell him that he is going into treatment. Tell him that you know that he has been selling drugs and that treatment is not an option. Jail is.
If you cannot confront him alone, and I certainly understand this, have someone else with you.
Don't expect him to respond rationally. He is not going to thank you. He is going to, at the very least, tell you that you are nuts and imagining things. He may walk out. He may or may not come back afte rhe does.
Have a bag packed and the treatment program notified, paperwork made out, etc. in case he does go along, quietly or otherwise.
Treatment is not a cure. Relapse rates are high. But it shows him the tools for sobriety, and if he wants to pick them up, now or later, he will know how.
Get to an al-anon or a nar-anon meeting, Go to a few until you find one you like.
Keep coming back here. There are moms in all stages of grappling with this disease, and there is a lot of wisdom - not all of it agreeing with any of my above suggestions, mind you -everyone is different, and ina different place -- but we all learn, and we don't have to be lonely when we do.
Everything is so clear to me in this 20-20 hindsight. But knowing it and being able to do it are different things. You have to be prepared to let him go, and that feels like wrenching a part of myself -- the heart part, I think -- out. It's a sorrow that only eases with our own recovery.
You did not cause it. You cannot cure it. You cannot control it. Even tho, as a Mom, I didn't believe any of that. Not in the beginning.
Prayers and many mom hugs to you ~ Nitelite