Sounds like she was probly fiddled as a kid tbh.
Yes because that happening to someone makes them want to sleep around
Although you want advice you really have to just go with your gut instinct. Otherwise people will give their personal opinions and you'll probably end up feeling even more confused. If you're not sure right now perhaps hold back for a while and not see her that much or not at all so that you can have time to properly think it through.
My only advice would be always follow your gut instinct.