Just saying... There's something called "delayed ejaculation", which is basically when a man has a problem in reaching orgasm. Thanks to people's wrong ideas on sex, many think this is cool, since the man can endure more time, but actually this can be pretty bad, as you noticed...
Treatment for this exists. It's often the same as the treatment for premature ejaculation, which is, basically, therapy (both regular psychotherapy and others), medications (both starting to take some and/or changing the ones that may already be part of the person's regular ones), avoiding some drugs and so on.
As for the comment that I talked about "eternal pleasure", I'm obviously not taking in account the body limits (and other things that may result in death and alike) for all participants, usually by "magic" or whatever the h-work uses as an excuse. Obviously that after too many time, without such "extra", it stops being pleasurable, but if such "breaking point" existed, any hentai about "they are still cumming after days/years being captive" would not exist (except for the guro ones), since the people would either not be cumming anymore, and/or they'd simply be too sick of it and would simply escape without coming back, instead of wanting to go back even before escaping (like what's shown on most stories with such plot).
