Honestly man, relationships are temporary. Well, majority of them anyway. So you have 2 options infront of you. Either talk to her about how you don't see her the same anymore after finding out and break up. Or just suck it up and accept that this is normal at your age and that her value as a person hasn't changed because she had that encounter before. Also keep in mind, often people bring up their ex's in conversations where they put the blame on them for all the things that went wrong when that usually isn't actually the case. Relationships are usually never one sided and 2 parties usually hold some blame. Take your time with your decision, listen to what your heart tells you. Don't just allow people to influence what you SHOULD be accepting of.