Why can't I orgasm during sex!!!

We could go for hours and he could cum like twice and I'd be bored out of my mind. Or I'd be sooooo close to orgasming and then he'd move and I'd lose it. Then I end up cranky cause I didn't get to climax. But when it's by myself it's so easy. I just don't understand. The sex isn't whack! What's wrong with me?