Clarity, I am so sorry for your pain and feelings of betrayal. I think you would be wise to focus on you and your son and not worry about "trying to help him through this." He has people in AA and presumably from his outpatient treatment who are WAY more qualified to help him than you are. If you really could "help him through this", wouldn't it have happened before? And did it?
Take some time to settle down, breathe, say the Serenity Prayer. And once you're calmer, try to think as rationally as you can about your options and what is best for you and your son. Do you have f2f support for yourself, like Alanon? That could be very helpful to you right now also.
I'm glad you're finished w/school for your new career; hopefully knowing that you are able to get a good job will help with the financial concerns you may have.