Girl that’s just a fact of life. Our orgasms are notoriously finicky. I mean for me personally, everything could be going right and then a sunbeam peeks through the curtains and hits my leg and I lose all momentum. I can simply sense a bug in the room and it pulls me out of it. I suggest taking some time to be present when you’re by yourself and see what’s making you tick and what gets you there. Focus on those sensations when you’re with a guy. Now… whether or not he knows what to do depends.
maybe spend more time solo connecting with your body. a drink or 2 helps me. not enough to impair you or anything just enough to calm the nerves. if you’re worried about how you look, it sounds silly but do it in the dark. just try to relax as much as you can. maybe have your partner massage u first, before foreplay is great.