Breaking up after 3 years?

My boyfriend and I have been together for 3 years and in a marriage-like relationship for more than 2. Everything started out great but I feel like we are just friends now (minimal sex). Everything he does bugs me. I got frustrated and cheated on him. It made me realize that things are not going to work. He tends to ignore our problems and act like everything is good. How should I bring the topic up? Should I bring it up briefly at first to give him an idea of what I'm thinking or should I just dive in? Im afraid to hurt him even though I know I will.