I'm 21 years old. I am in a relationship with an 18 year old girl and I have been for 1 year and almost 2 months. We are both deeply in love and we love to spend every second together. In the very beginning of our relationship we had some cheating problems on both ends. We both have gotten through them and now tell each other everything.

She has recently admitted to me that during one of the times we were having sex she thought about my friend and what it would be like if he was on top of her! I was pretty much outraged at this and I didnt know what to say or how to act. She was a virgin until me so could this be the type of thing where because she doesn't know anything about having sex besides with me, she is seeing what it would be like in her own head? She said that the thought was very brief and that she doesn't know why she had that thought.

I have asked her if she has feelings for him and she replied, "Definitely not". Should I believe her on this? Please help me because I dont know what to do!!