I applaud you. You recognize your 'bottom line'. You are getting in touch with your boundaries. Good for you. You are incredibly strong - know that!
A couple things you describe sound exactly like experiences I had (at 27) with my SO. Looking back, I wish I drew the line like you have. Now, I'm married w/ kids and separating is extremely difficult.
You care for him a great deal. Severing an attachment is very hard. It takes time. Talk to him if you need to, but please do not put yourself in harms way.
Oh, and yes, you are NOT doing anything "to him". He is self-sabotaging. It's about his internal struggles and not about ONE THING you've done. Please remember that.
Take good care.