amazing, most perfect fiancé..but the sex life :(

When we first got together our sex life was amazing, but in the last year our sex life has fallen so badly...I'm talking...once a month if we are lucky.. I don't even try anymore because when we do he cums super fast and I'm left just dumbfounded. He has tried taking over the counter supplements and everything inbetween, and he says he's just so turned on he cums fast and he doesn't know what's wrong where he doesn't have the want to have sex. I've gained a few pounds, and he ALWAYS makes me feel beautiful, but this is making me think it's me and idk what to do! He says he doesn't want to get me pregnant before the wedding, he says so many excuses. I just don't know and I feel like a BITCH because our relationship is amazing in every other aspect, except sex. Anyone else have this?