O.K., here's the deal. The harder you try to come, the less likely are your chances. The mind needs to be totally relaxed in order for an orgasm to occur.
The chemicals that circulate in the body when you are worried are incompatible with the chemicals that are required for a person to achieve orgasm. So relax.
Skip the sex olympics. Practice masturbating on your own, and make sure you know what turns you on. If you can come on your own, then you should be able to show him what works.
If you can't come with him, even after you are able to get yourself off, then you might want to look into the possibility that you are actually not allowing yourself to let go with him, and this is an emotional issue.
If it turns out that you are holding back with him for emotional reasons, then figure out what the issues are. Are you afraid to be vulnerable, to give yourself over, care too much and then be devastated if he dumps you? Are you afraid to look foolish when you orgasm?
Once you figure out what the block is, you are on the path to healing it. Best wishes.
