He should see a doctor if he thinks there's a problem. If he doesn't think there's any kind of problem, obviously you DO think there's a problem and him not seeing it (or not facing it) is a problem in itself, in which case couples therapy or other therapy might be called for.
My intuition tells me it's a relationship issue. Why do I think this? Because you are very upset over it, you post in bold type, and you seem almost hysterical. This suggests to me that you are putting a lot of pressure on him to get erect and "perform" for you during sex---which might be the very thing stressing him out of a satisfying sexual encounter with you.
Relax! Let him be what he is. If he doesn't cum with you or in you, it doesn't mean he doesn't like you. It's possible he has some sexual fantasies or turn-ons that he prefers to do, that he's embarrassed about doing with you or telling you about. If he hasn't been intimate with a woman very much until now, then he's probably been masturbating to whatever turns him on for years. It can be difficult for a male to relinquish the personal rhythm, friction and fantasies that he's used to and engage in a very different kind of sex where he's dependent on your rhythm and your ways of doing things. I'm sure he senses your worry and impatience and experiences it as a demand, which can certainly cause a loss of erection. He might not even be aware that your impatience is because you feel fearful of being unwanted if he doesn't sexually perform (if indeed that's true).
Try some exercises where you each write down sexual fantasies you have (or are curious about) and then share your lists with each other. If they're impractical to do or a true turn-off for one of you, then try watching them on porn together, or just let him masturbate once in a while. There's a huge range of human sexual behavior and preferences. You just need to find some sexual common ground.