She's been with bigger

Hey guys first post here, I could use a little guidance.

Me and my girlfriend were together for over 2 years. Here's the story...

After our first year of dating we were fighting a lot. We are both head strong people and very argumentative. We are deeply in love though and have a lot of fun together. She is head over heels in love with me and I love her very much but she is my first girlfriend so I have always wondered what it would be like with someone else.

Anyways after that first year, I graduated college and did a Euro trip for a month. Before I left, we left things kind of in Limbo, where we weren't really broken up but not really together. During that time in Europe I slept with someone else during a stupid one night fling. When I came back from Europe, I couldn't tell her.

We got back together and everything was perfect but then I found out she had tried to sleep with someone else too when I was in Europe. We split up for good for about a month during the summer. It was the worst month of my life. I was very very depressed. I don't drink a lot and she was out partying and drinking heavily pretty much every night. After a month of me trying to win her back I finally told her I had to cut all contact with her and move on. After I said that, she called me the next day wanting to get back together saying she couldn't imagine her life without me. So we got back together for almost another year and everything was great until...

I found out she was having sex with someone else while we were on our official break up during the summer. This killed me. Literally killed me. I had gotten a BJ from some random girl during that time but it was a shallow empty thing I had done. She had slept with this guy several times. I had a feeling she had initially, so when we got back together I kept drilling her with questions but she always denied and denied. I then found out through her text that she had been sleeping with the guy 2 weeks after we broke up and he had a HUGE penis and was really good in bed. This guy had slept around with some girls she knew and pretty much only banged him because of his Apparently it was very thick and big and he was a great lover because he was very attentive to her in bed. To be honest I have only an average size penis so this kills me.

After finding this out I had to end things. I feel like I can never get that back. I feel violated. After interrogating her with questions she had admitted that the sex with him was physically better but not emotionally and his penis is much larger than mine. Like porn star status. I'm extremely upset she lied to me when I first asked her about him when we got back together. It sucks because we've been so good for the last year but after finding this out, I don't know if this can ever be fixed. She is absolutely in love with me and wants to get back together but I don't think I could ever get over this. Am I being stupid?

I really miss her and NEED YOUR HELP. Please give me some perspective on the situation. She really really wants me back and I just don't know if I ever can. I think most of you will say that I'm being stupid but please understand that I would have to live my life knowing she had sex with a huge penis, liked it and bragged to all her friends about it. I can't stop thinking about it and don't think I could ever be 100% in the relationship. Please help.