My girlfriend [21 F] wanted us to swing and I [21 M] broke up with her

We used to study at the same college and one day she sat next to me in the bus, I got her number and we started to see each other every day, I was deeply in love with her and we used to talk about getting married, even though we only spent two months and a half together. At first she seemed to be a decent girl, but after a while she told me she had sex with couples twice before dating me and that she wanted us to have a threesome with a single girl, I really liked the idea and we started to look for someone interested. The following week she told me that we would only have the girl if I accepted going out with couples too, and I said OF COURSE NOT, I would never ever give the love of my life to some random guy do her in front of me, just the fact she suggested that made me DISGUSTED. What kind of man would do such a thing, seriously? One day I told her I would feel safer wearing condoms but she replied that the pill was enough. Then she made this comment "Relax, I lost my virginy at 12 and I only began to take the pill when I was 14, I've never gotten pregnant", I imeddiatly replied "and how many times did you have sex until you were 14?", her: "I really wasn't a prude". That conversation made even more DISGUSTED. She kept insisting on us having sex with another guy until I got mad and she dropped the subject, but I was very hurt already. Time passed and we got over those arguments, the relationship was going phenomenal, we were so happy together, but tables turned when I saw an old picture of her having sex with that couple she told me about, that image got stuck in my head and I used to cry a lot about it. I asked her at first to delete it and she refused to do so, then the next week I got pissed off about it and she deleted it, but not after hesitating. I mean, really, I HAD TO ASK THREE TIMES for her to delete a picture of her doing another guy, I feel so DISRESPECTED and I feel she's not decent. I was in love with her until that very day. The last day we spent together we hugged each other and discussed all the issues we were having, we both cried for hours and agreed to start from scratch, I tried hard to forgive her, but I just couldn't take the pain anymore. The next day I woke up with my chest so tight, I cried a lot for the pain she had caused me, then I texted her saying "thanks for all the great moments of joy we had together, for all the nights of pleasure, for all the love you made me feel, thanks a whole lot for having become part of my life." Then I texted "I just can't do this anymore, I'm sorry". It's been three months since we split and stopped exchanging messages. I MISS HER A LOT but unfortunately she is unfit for a serious relationship. If she was decent, I would have married her for sure. I'm still hurt and I can't forgive her, just wanted to get this off my chest.