How to break up with him?

I have tried breaking up with my boyfriend before but his reaction is dreadful. A couple weeks into the relationship he told me he lives for me because im his only happiness. But he is very inconsiderate, immature, and not emotionally stable. When I tried breaking up with him the other day, he tried salvaging it by promising me to be better but he has promised that 3 times before. I kept telling him its done but then he started to call me and he was sobbing and telling me he is worthless and that he is gonna cut himself until he bleeds. I was genuinely worried so I drove to his house, only to find him perfectly fine, not a single cut on him. But I didn't want to say anything in case it triggered another episode. I have no idea how to get this baggage out of my life. I tried helping him with his mental issues and self esteem but he doesn't wanna help himself. I used to feel pity but now I feel idiotic for letting him get this far with me knowing he is just doing it for attention and self pity, with no real interest to be happy or make others happy.