How should I go about this friendship?

I've had a friend since highschool. We both like a lot of things and we have had our own issues, as many friendships have, but we make up and keep going. We both live lives where mine tends to be a bit more managed and easier compared to his own. That's not me bragging, I mean that because many times, and this is the reason for the post, I'm the one he goes to financially for help. Now he's had a rough childhood, and being autustic is something that's had a hand in it, especially with brothers who aren't reliable, with just a few family members he can rely on.

The problem? I tried setting a new years resolution to STOP helping him because slowly resentment has been building, and I know he isn't trying to do this, but life seems to keep screwing him over to where I'm in a spot where I feel like I need to help or he could suffer. I struggle with controlling my emotions and become more stoic, but when I cave and help out? I feel angry at him and myself because I couldn't stick to my boundary. No matter how much I try, it all seems to cave in with me helping him, and I'm so tired. I've honestly hit the point where I'm not excited like I use to be when talking to him, and the anxious feeling I get when he might call is noticeable. The answer seems so simple and obvious, but I keep holding on for some reason and I don't know what to do. Has anyone ever felt this way?