How to break it to my boyfriend?

So me and my boyfriend have been dating for 3 months now and we've gotten pretty serious. I love you has been said at least a hundred times. But for some reason, I've been having some serious doubts. I do care about him, but somehow being with him just doesn't make me happy. But I'm scared because I think something might be wrong with him. If I even suggest taking things a little slower, he might go in to a depression. I know, it sounds a little far fetched, but we were friends b4 we dated and i've seen him go through breakups. And I think he's a little obsessced with me. What would happen? I feel stuck in a strange relationship I want out of, but don't know how. If it were a normal guy, I would easily break it to him and we could both recover soon. But him, I don't know...so if you could give me some pointers, i would really appreciate it. Or better yet, give me some tips on how to grow closer to him so I don't have to? I feel like a jerk, but I don't think I am. I just want this to go as smooth as possible. Thanks.