Indeed. See a therapist and talk about this stuff. Make sure you talk to your gf. Explain what is bothering you and that you need to step back from the relationship. But make sure you tell her in detail that she did nothing wrong and this is 100% a you problem!!!

As I said, everyone has a past, are you saying it would bother you more to not know what happened than it does to know? What about her? Does she know about your past? Is she allowed to feel the same about you? Honestly, it seems like you’re super immature and, in no way, ready to handle a committed relationship.

Eta: regarding you meeting the other dude. If she purposefully introduced you to him then that’s messed up. But if you were at a party that he happened to be at and she couldn’t avoid the meeting then, again, it happens.

Everyone has a past and it’s likely that any girl you’re with now or in the future will have had someone “better” than you. But she’s choosing to be with you and that’s what matters. She could have stayed with one of those other guys but chose you instead. Pull your head out of your ass and move on or you’ll lose her. You should definitely see a therapist. Also, QUIT HAVING DETAILED CONVERSATIONS ABOUT PAST RELATIONSHIPS/HOOKUPS FFS!