My boyfriend is threatening to harm himself if I break-up with him?

My boyfriend and I have been going out for about a year and a half and we've been friends for 6 years and have a long history together. This is my boyfriend's first real, committed relationship and he has some abandonment issues because of his mom coming in and out of his life during his childhood. He's very clingy also and has given me a ring that he wants me to wear on my engagement finger even though I'm only 19. The problem is, for the last few months, I'm starting to see him more as a friend and I've been hinting at maybe taking a break to see other people and see what happens. He won't hear it though, and pretty much won't let me break-up with him. Every time I ever suggest it he pretty much ignores what I'm saying and convinces me to stay with him. We got into a fight yesterday and I said that maybe we should break-up but he started getting really mad, then he cried and threatened to kill himself. We've talked about what would happen if we broke-up in the past and he said jokingly, that he would destroy my property and be the cliche crazy ex boyfriend. Now I'm starting to think he wasn't kidding. I feel trapped, because I want to be happy and I would really want to still be his friend if we broke-up, but no matter what I say, he still says we're together. Help?