Well, do you mean you can't orgasm in his presence? Or during oral sex? Or during intercourse?
if you can't orgasm during intercourse: join the something like 85% of women who can't. There's nothing wrong with that, because frankly, men and women are poorly designed when it comes to female orgasm during
sex. Most women just don't get enough clitoral stimulation. Try what most do, use some sort of manual (toy or hand etc.) stimulation during sex.
If you can't orgasm during oral sex, just try relaxing. Don't concentrate on the goal at the end, enjoy the sensations and feelings that you have along the way. While doing that, you might be surprised at what sneaks up on you (psst.. like an orgasm.)
If you can't orgasm at all with him in presence, try some alone time with masturbation. Figure out what you and your body really like, then try as above, just relaxing and enjoying what's going on.
I would estimate that orgasm makes up maybe 10% of the total sensations of sex. People are so goal oriented, thinking about orgasm, that they miss the other 90% of what's going on.
Sex is soo much more than just orgasm. And if you just relax, and enjoy the 90% of those feelings and sensations for what they are - good feelings and sensations - you might be surprised to see, lo and behold here comes the other 10%.
BUT, you that's not important.
Enjoy sex for sex.
NOT sex for orgasm.