Breaking up a long term relationship

I've been dating my boyfriend for almost 2 years now, and last year he gave me a promise ring which I accepted, around that same time I was also diagnosed with serious health issues-- and he has been there this entire time, so we've been through a lot. He says he plans on getting married but I am just so torn right now and I hate it, he says he loves me so much and I know it would kill him if I left but I am miserable--let's just say the term "I love him but I'm not in love with him" is completely accurate. His family loves me and I love them but I don't know what to do because I catch myself thinking about our future together all the time but I also feel so incredibly stuck-- like I'm in limbo with my feelings. I know it isn't fair to him, but whenever I bring up the suggestions of taking a break or anything remotely close he reacts horribly. What do I do :(