There is a lot if info on the Sex Talk FAQ, including threads on taking forever to cum and trouble cumming with a woman.

As you can see, it's not uncommon. Please read both threads with all their links.

It may well be very helpful for you to re-condition yourself - those links go to various masturbation sites as well. If you skip cumming for a couple of days and refuse to rely on your habitual technique, you will eventually have to get off with different stimulation. Go to milder porn and then eliminate it for a while. Get so that a wide variety of stimulation gets you off, including slow, wet, gentle things that more closely simulate intercourse.

By the way, for a lot of men, if not most, it is harder to get off with oral sex than with intercourse.

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