I have that as well. It's performance anxiety for me so maybe it's something like that for you as well.

I can even feel it kicking in. When I'm close to orgasm, I can feel my body start to hold back or ... shut down a little. It comes from fighting a combination of years of focusing on my wife during sex instead of just enjoying it and then a few years of anorgasmia caused by medications. Now I can have an orgasm from masturbation when I'm alone, but in the context of sex the performance anxiety kicks in and I can't have an orgasm.

There's ways to work through it, but since we've gone to an essentially sexless marriage it doesn't really matter anyway.