He needs a urologist who specializes in erectile dysfunction. I've worked for urologists, and they tend to specialize within their specialty, so if you call one urology practice and ask if any of their doctors specialize in ED, the staff that answers the phone should be able to tell you which MD to see, even if it's not one in their practice.
Some people have trouble saying what the appointment is for when they call; they only want to say it to the MD, but different appointments take different lengths of time, so we had to know what slots to offer. (We weren't being nosy).
Before you go running off to the doctor let's think about it. You say he has no trouble maintaining an erection, so he does not have erectile disfunction. Erection and ejaculation are two entirely different things. There are no medical problems that will delay ejaculation. It can be one of two things. Either it's a psychological thing ("performance" issues) or he has a decreased sensitivity in his penis. Most likely the latter.
Is this a recent thing? Can he ejaculate in a "normal" (God, I hate that word) time when masturbating? Are you lubricated enough? Are you lubricated too much? These are questions you have to explore before you go looking for a medical cure that just isn't there.
Trust me, I'm not running off to the dr, it's been a really long time coming. He used to be able to ejaculate eventually while masturbating if he was looking at porn. But we weren't having sex... ever... so I put a stop to (with his reluctant cooperation) the porn. We have locked the computer so he has no access, and since then hasn't been able to ejaculate at all. The big problem is, we want to have a baby, but if he can't ejaculate it's not going to happen! Besides the fact that if he were to be able to do so, our sex life would definitely improve (it can't get worse) which would be great for both of us.
I didn't know if the urologist could help us any or not, but I am truly desperate. We've talked about going to therapy together and he finally agreed, but I'm not sure that it will work either. I'm stressing about it so bad, I want a baby desperately. Wish us luck!
It sounds to me like it's most likely psychological. If he can ejaculate while masturbating with porn I think he might have some issues. (Is he unsure about getting pregnant? Afraid?)
Therapy sounds like a good idea but I'd recommend he go alone at first. Therapy only works if you can open up and be honest, easier for him to do if you're not in the room.