Frustrated

My fiancée of two and a half years is my best friend, he's truly wonderful and I love him more than anything. But I have a way higher sex drive than he does, and it sucks!!!!! I mean I'm lucky if we have sex once a week. And when we do, it's good, but it never lasts longer than five minutes, usually less. And I never get to orgasm. I'm the only one who initiates, it's never him. I've talked to him, and asked him if it's because he's not attracted to me, or if it's not good for him, and he said that's not it, it's just that he doesn't want sex that often. It's just so frustrating!!! I masturbate sometimes, and I can get off on that but I want sex!!!!! Anyone else have this problem?