Infedelity

My girlfriend and I are going through a real roller coaster ride and I need advice. Let me give you an insght how it all started. We met on a dating site. I am from California and she is from Chicago. We talked over the phone where we shared a lot of common intrests. What I really liked about her was her trust in God, apart from all the other things we shared in common. We talked about our past relationships and both agreed that we had learnt a lot from it.
She told me that I was the second guy in her life. That really did not concern me as we all have a past. So we were talking marraige in time and planning our future. I flew down to Chicago to meet her and it was like a dream come true. We attended church together to get God's blessings. I promised god to marry her if that was his wish. It was a week of something wonderful we both shared. Cutting things short, after I was back she called me up and said she was not completely honest with me. She had been with another guy who apparently just happened. So that made me number 3. That was not a big deal. When I asked her why she was tellin me now. She said the guy wanted to marry her and was gonna send me pic of them. So she decided to come clean. She was not completely honest thou. It is only after questioning that she told me that she had met with him again straight after I was back and spent the night with him at a hotel. She swears that she did not have sex with him and that they only had oral sex. She says she wanted to be honest with me and make our relationship work. I am so confused and devastated I dnt know what to do. I have forgiven her and asked her to ask forgiveness from God. However, I cannot seem to forget it. I have lost all my trust in her. I have lost sleep and the thought of her with the other guy in bed come to my mind and disgust me. I don't know what I should do. Please advice. I can use all the advice I can get. If I accept her back will she be faithful or is it a big mistake. Help me please

The only reliable approach of you dilemma is: trusting your gut feelings. You sound like a sensible, moral person, and clearly your girlfriend is not playing the mating game on a level playing field. What's happened may, or may not re-happen, but your trust in her will never be complete. if you can leave with that, and feel she's sincere when asks for forgiveness and trust, then go ahead with the marriage. If this unreliability is a big issue, and you feel she's not genuinely committed to you, then you need to face downgrading the relationship to simple dating or friends with benefits. If anything, this downgrading will help you gain her respect (guaranteed).