Confused can someone please help me?

So my girlfriend and i have been dating for a little while now, she is mildly retarded and her parents said it was ok for us to date, but today was our first time making out, and something just wasn't right. #1 i thought she was a virgin, but i found out that she clearly wasn't, # 2 after we finished i asked her was their someone else that did to her what i just did,she said she wasn't suppose to tell, i told her it was ok if she told me because i am her boyfriend now, and she just started screaming and crying hysterically, it took me every bit of 30 Min's to calm her down. i really care about this girl, but i don't know what to think, i believe some one possibly d her, but i don't know for sure, what can i do, please i really love this girl.