whew people are tearing you apart here huh. Well here's what I think.

Your feelings are valid, from what you have typed it seems that you are more relationship minded whereas she obviously wasn't. This huge difference can and will cause rifts in a relationship so here's what I would advise. Take a second to reevaluate your relationship and in particular how she treats you outside and inside the relationship. A big reason imo why guys don't like promiscuous girls is that they are afraid that they are going to be the safe option, the guy she chooses not because she lusts and loves him but the guy that is stable and dependable. That's why I would advise looking at her actions during the relationship.

For outside the relationship, does she initiate dates as often as you do? Does she give you gifts randomly without you asking? Does she prioritize your needs (within reason of course)? Does she in general want to be around you? If you can answer yes confidently to these questions (and similar type of questions) then you can know that she loves you. However love is just half of the equation.

For inside the relationship, does she initiate sex often? Is she enthusiastic about sex with you? Does she indulge in your sexual fantasies? Does she just in general get aroused by your physical body? If you can answer yes confidently to these questions (and similar types) then you know that she lusts for you.

After going through these questions if you come to the conclusion that she loves and lusts for you then I would say that you don't have to worry about anything (of course this is all assuming that you are doing your part to show that you love and lust for her). However if after all that you still feel insecure about her past then I would say its best to talk with you directly and see if she can help you get through this. If even that won't help you then I would say its break up as this will be something that causes resentment and rifts within your relationship. Whatever you choose I hope things go well.