<human>: I've been dating my current girlfriend for about 2 months. To begin the story, we have to travel back to before we were dating.

2 weeks into knowing her, she started talking to her ex boyfriend and they eventually hung out and did some sexual things (not sex, but along those lines). She told me the next morning and seemed very upset and genuinely apologetic. Except there's a problem. She told me that they only kissed. She didn't mention anything else they did. 

Last night while we were on the phone, she told me everything that they actually did and I'm completely heartbroken. I feel lied to and cheated, but they did this before me and my girlfriend were even dating, and we barely knew each other. Today, I was extremely mad and upset and I told her how I felt about everything and it got her upset, so now we're basically mad at each other. 

The problem is that I feel like I'm in the wrong. She didn't do it to hurt me and she didn't tell me everything they did because she wanted to protect my feelings and she didn't want to lose me because she knew that she really liked me. I really just want to call her and apologize and try to make everything okay, but I feel like what she did wasn't okay and I need to show her that she was wrong. I'm really conflicted and I just need some advice from you guys. Thanks for taking the time to read.

Give me the gist of the text in a nutshell
<bot>: My current girlfriend hooked up with her ex-boyfriend before we started dating. She lied and said they didn't do anything more than kiss. Am I in the wrong for being mad/upset?