loose

My boyfriend and I have amazing sex, we have very good sexual chemistry and have sex very regularly (anywhere from 2-6) times a week). Although I am 24 and have had a few partners before him, he was the first to ever make me squirt (I had experienced orgasms before but not squirted). I've told him but he does not believe me and says it impossible that I haven't done it before. Anyway, about every month or so, we will have sex and after asks if I had cheated on him, he says that I feel loose and he can tell a difference and that he isn't dumb. He says that if we haven't had sex in a few days and I should feel tighter. 

I know that he is completely wrong, I know how a vagina works. I just really need help on what to do or say to him. I truly love him, we live together and have a life together and I would never cheat on him. When he tells me I'm "loose" it completely kills me and I lose all sex drive, affection and makes me very self conscious. When this happens I tell him how horrible it makes me feel and that I would never cheat. We usually don't talk for a few days. He makes it out to be my fault but it's not and when we make up I'm always the one to buckle because I can't stand fighting because we are very affectionate people.