My boyfriend(19) threatens to end his life everytime i(18) try to break up with him

I don’t know what else to do. I do love him, but I feel like sometimes he’s a little too invested into a relationship for how long it’s been considering. We’ve only been dating for around eight months and not to say that I didn’t play a part into it considering we are dating and I would assume that we talk about things like that but he’s talked about marriage and talked about kids and how he’s never gonna date anyone else but that if I left that he wouldn’t know what to do with his life and before he was just depressed and all of this stuff and it really does scare me, but there’s been times where I’ve tried to break up with him and he would just freak out and blow my phone up and he would just say things that indicated that without me he would just do something crazy and it scares me so bad and I don’t know what to do. even when I wouldn’t try to leave, he’d tell me things like if you left I wouldn’t know what I’d do and stuff like that and the other day I had posted on my Instagram note saying. “I’m trapped” and he replied to it saying “I’ll break you out” because I have been in the hospital for the last two days and he assumed I was talking about the hospital, but when I saw that he replied to it all I wanted to say was I meant in our relationship but I don’t wanna hurt him and I don’t wanna hurt his feelings, but I don’t know what else to do. Please give me brutally honest advice.

TLDR

I’ve been dating my boyfriend for ~8 months. He’s already talking about marriage/kids and says he can’t live without me. When I try to break up, he blows up my phone, freaks out, and hints he might hurt himself if I leave. I feel trapped but also don’t want to hurt him.