That's totally normal. It took me months of masturbation to *ever* be able to cum with a partner.

Think about it this way: if you can cum from masturbation, you will probably need the same type or similar stimulation, position, etc to do it with a partner. So if you're on your belly and humping something, you'd have to do that with him (can be tricky but doable). If you're on your back, rubbing your genitals with fingertips in circles, again the surest way is to do that with him.

I find that I have an easier time up top, but I need to be able to rub my cock against his pelvic bone to get the right stimulation, and he can't move because that will throw me off the spot.

What you're going through is totally normal and tons of people are in the same boat, but it can be done. People who aren't cumming during sex are usually thinking they can use a different type of stimulation than they would during masturbation.

The secret is using the *same* stimulation. There's a reason you do it that way. And tell your partner not to move while you're doing it. Get into the right position and just keep going.