No easy task indeed. Has anyone gone through it before?

I'm starting to not have the feelings I used to have with my boyfriend. We've been together for 4 years. He's sweet and everything but some things just bother me. I am not attracted to him anymore. Just lost interest the last couple of months. He's thinking about marriage...I can not see myself spending the rest of my days with him. Thats how I feel at the moment. He's done nothing wrong...more so me whose done something but I am not going into it. I just don't know how this is all going to plan out :/