just get over it before it eats you inside
she didn't make a mistake being with the other guy or guys, she was becoming the person you know now... what would you change about her (personality wise)? hopefully nothing... well if you were to remove the other guys, you'd be with a completely different woman...
so... move on from it... concentrate on why your together, not why she was with other people.
and yes she's with you for some absurd reason... if there were no reason she wouldn't be with you, and if it was logical i don't think it'd be love
again concentrate on making this the BEST relationship for her to look back and analyse, and she probably won't have to