No, it isn’t normal for him to vomit after sex. By vomiting, his unconscious mind is symbolically throwing up feelings that he can’t tolerate.The only real way to figure out what these feelings are is for him to begin psychoanalysis. He clearly is suffering from a deep-seated conflict, and the problem will not get better on his own.Even if I were to speculate on what the unconscious conflict is about, even if I could guess what feelings he is trying to eject, he is the one who needs to form this understanding, not I.So, tell him to begin psychoanalysis at once. Once he identifies the issues and feelings, he should be able to work them through via talking therapy.