girlfriend looked at Facebook messages. HELP?

[Aaron]

Hey guys, I've been dating my girlfriend for over 5 months now, and things have been going awesome. We spend a lot of quality time together and have grown together closely. A few hours ago, she came by my house when I was at work, since she really missed me. I come home to see that she's acting strange and wants me to sit down so that she can talk with me. She started telling me that she read my Facebook messages on my computer.. Here's the thing. I've been talking with other girls sexually, saying that I was single and wanted to have sex with them, etc. However, I have never cheated and only did that to get attention from them.

My girlfriend has a lot of guy friends and I get insecure. I just wanted attention from other girls but I never had thought of cheating on her. She just left a couple hours ago, in pain, anger, and in tears. I really don't know what to do at this point and realize how much pain I have brought to her.

I really want to make things right again and show her that I can be trusted. I do not want to break up with me because I really like her and care about her. What should I do? Should I wait until she contacts me? What can I do or say to make things right? I'm at such a loss right now and realize I have brought so much pain to my girlfriend. She just texted saying she wants to break up.