I have the same problem, though because I'm female it's a little different of course. I'm not sure what my problem is anyway since I'm not on any medication that would cause anorgasmia and it also takes way too long sometimes when I'm on my own. Actually, it started taking longer after I started using a vibrator which was supposed to HELP.

And I feel so guilty because it makes my partner feel inadequate and because I'm afraid it's wasting his time since we sometimes try for hours because I feel like I'm about to have an orgasm for that long and don't want to just give up.

I don't know what the answer is yet, but I just wanted to say I could relate.