First of all, you are an angel for staying by this man. I assume he has no one else in his life because he can't keep them there, no matter how much he wants others. He definitely acquired this schizophrenia from his crack addiction. He overdosed a few times and absolutely shrunk his brain. Forgetting simple things from one minute to the next: classic example. Yes, he probably still has some intelligence, but he can't sustain thinking long enough to really use it. I don't want to depress you, but I'll bet he is an emotional black-hole - he probably cannot really feel empathy.
All this is heartbreaking to eventually realize, but it seems he might be so far gone that he doesn't know it?So, what can you do? How can you help? I beg you, don't abandon him! If you are concerned for your safety, then obviously stay away, but check in on him! He can't possibly have anyone else in his life that cares for him like you do, even as a human - Please, make him know that he is loved by at least someone, no matter what! On the other hand, it might help to be a little firm with him, to make him confront the fact that he is having delusions. I honestly don't think medical help can really help him, unless he becomes homeless. The point is not to make him catatonic - he is still a human and has a right to his thoughts - but I think he could probably, at the very least, use an anti-depressant to alleviate his anxiety.
You say he has a big heart: that means he always did and he still does have that as a part of his identity. Trust me. Just for that, I think he deserves your friendship and understanding. Don't waste your life caring for him (unless you have nothing else...would he be so lucky!) but please, as a human, continue to play a role in his lonely, short-term life (I am sure he knows that something is wrong with himself).