What would cause a man to not come during sex?

Well,if you don't sperm during sex your going though menopause

too much masturbation is one cause as well as some medications can prevent men from ejaculating.

Hello lovelyone05, I'm Dr. Steve Mahannahan.
I have read into your question and I've come up with the logical answer.
There are many factors in why a man will not experience an orgasm during sex, however, the most occurant reason for this is because the man you are having intercourse with is actually a woman. Most people assume if it has a face it's a guy, but this is common misconception. Check the genetalia, if you aren't sure, check again. -Dr. Steve