When I first began playing with toys and masturbating, I found there was a way I could get off by myself extremely quickly- it involved using some kind of buttplug or dildo in my ass while using a vibrator on my clit. I would usually cum in less than a minute. Taking this into the realm of sex with a partner- I found that the easiest way for me to cum with a guy is through anal sex with him rubbing my clit. Now, it's not the only way... but you can try taking it one step at a time. Easy parts first just to get over the anxiety. Next maybe just try lots of deep anal sex with no clit rubbing- I also finds this gets me off really easily too. From there then maybe progress to try to get off through vaginal sex, etc.

Sometimes just getting past the initial barrier of cumming with a partner can help the mental aspect. And yes... having the right mixture of dominance involved is key as well. You need mental seduction even more than physical.

Good luck, and don't give up!