I need to find a way to break that to him tomorrow while letting him know that I still believe he can get help, and that I'll be here (as a friend) should he ever decide to get it.
Speaking as someone who went through two broken engagements before getting married, (I broke up the first one and he ended the second), I can say the kindest thing you can do for him right now and for yourself is to go no contact. When you say, "I'll be your friend" all you're doing right now is letting him know that the door is still wide open, and he's just going to waste time and energy trying to get back together with you when he should be working on himself. Water can seep through the smallest crack - you've got to seal that right up.
There may be a day when you can be friends - but honestly, I don't think _you're_ ready for that yet. And that's perfectly OK. He's been dictating every stage of your relationship so far - he should understand (not that he actually will) if you want to take the time to heal . Even in the most amicable breakups, both partners need to give each other some space. It just turns nasty when one tries to dictate the other's timeline.