cant get over my girlfriends past...please help!!!?

[Bryan]

okay me and my girlfriend have been going out for about 3 months now, were both 17 and we have sex regularly. i was a virgin before her and she has been with 2 other guys before me. until recently we have had a wonderful relationship and i love her with everything i have. the problem started when we started talking about each others past. she told me how long her ex's were with her and etc.. but the more we talked about it the more i felt challenged to live up to there reputations and more. and since she was my first it makes everything harder for me. i have low self esteem already but i feel like im not as good as them or idk. at one point i got so frustrated/ curious that i asked her if i had a bigger penis than the others. but my main concern is i CANT stop thinking about the other 2 guys, whenever we lay in bed, whenever i see her, all i think about is them having sex with her. i feel anger mostly, because she was stupid and young at the time and the way i see it they took advantage of her. but the detail she went into just stuck in my head the minute after she told me. i cant stop thinking about the things they did. and i feel its making our relationship slowly fall. i dont look at her the same, and when we have sex now all i think about is the comparison of me and the other two. i dont know what makes me so sad/angry/confused about it but something has to happen. the way i see it i feel like i need to just confront the other 2 guys and beat them senseless, and though i know that wouldn't help anything thats what i think. the worst part of it is her ex lives right next door to her so its indubitable to think they dont see each other walking to there cars, etc. anyway what can i do to get over this feeling? i cry about it all the time now and i cant even eat without thinking of those other guys having there way with her. please help me and dont say to break up thats not even close to an option. thanks ahead.