Boyfriend not wanting to have sex

Okay I have never posted on here before I usually just read but I need advice and have seen similar post ms about this before, so me and my partner have been together for over two years and in the first year we couldn’t keep our hands off each other and would have sex like 5 times on the days we would spend together, and since last summer things have changed like it went down to about twice a week and now i can’t even remember the last time we had sex. It makes me feel so insecure because I know I have put on some weight in the past year and my belly fat has gotten bad but when I have questioned him about it he says he likes my fat and doesn’t care about it but I just don’t understand where his sex drive has gone, whenever I try to have sex with him he says no and it just makes me feel so shit. So what should I do?