
Be honest with yourself. Is sex really important to you because if you are never going to enjoy it with the guy and he won’t want to do it if you’re not into it(hopefully). So if you’re ok with just a romance and not a sexual relationship then you can make it work. But if it’s not something you can look past maybe reevaluate the relationship.
try different positions, or cock rings/enhancers. Also, are you ONLY doing penetrative sex? if so, try something else. Have him eat you out, finger you, use toys, etc. It's not wrong for you to feel that way, but it's also not a a fault of his to have a different body part than what you expected