It is not the "not getting sex" that is traumatic, it is that that experience equates to "I am not lovable" for many men. It's particularly harmful when you see proof that other people are "lovable" and you're not. You feel like there is this world that you're permanently shut out from. Talk about it with adults and successful kids you get told "not to worry about it", "be yourself". You have a problem shared with many other people but you feel alone because (until recently) this problem hasn't been acknowledged.
These negative emotions persist into your college years, 20s, and even longer and sabotage your success with women and domestic life not to mention work and all areas of your life. Even when something good happens your are inclined not to believe it because of what you have internally and the resulting effect is self-reinforcing.