I hope knowing others share your heartache and sadness will help. You're still so young - you can't let this haunt you forever. My son is now grown, & I wish I could have back all the years I spent in misery and regret. We can't help them if they refuse to see what needs to be done.
Have you tried Al-anon snowfall? I wish I had given it a shot - I didn't reach out the way I should have.