Let me commend you for ruling out a medical problem.
From reading your post, the problem is almost certainly "Performance anxiety." Anxiety can become a downward spiral in which worry hurts our ability to focus, which hurts our performance, which makes the anxiety worse...
It's great that you're concerned about pleasing your partner. However, it sounds like you're one of those few men who needs to move a little in the opposite direction. It sounds like you're so worried about pleasing her that you're getting caught up in the "Performance" rather than just being in the experience.
First of all, there's nothing abnormal about a man not having an orgasm 100% of the time. Secondly, if you're having an orgasm 90% of the time, that means everything is working like it's supposed to. Most sexually active men won't have an orgasm at least occasionally.
My advice to you would be to just concentrate on being totally present in the experience without taking it toward a specific goal. We can't will ourselves to orgasm. I bet when you begin relaxing and just enjoying the experience that this will diminish. In other words, I think you need to be more IN the experience instead of trying so hard to direct it.
FYI, sometimes when you deliberately delay your orgasm to give your partner an orgasm, sometimes you won't have an orgasm at all. You didn't mention doing that: I just thought I'd make you aware.
I don't think I've ever met a woman who has an orgasm 100% of the time. Don't consider an experience a "failure" if she doesn't, or if you don't, for that matter.