Wow, thank you very much! You really laid everything out in front of me. Here's something I didn't mention:

My ex boyfriend was a real jerk. He hit me, pushed me, made me do things that I didn't want to... or basically, completely abused me and shot me down. One night, I sought comfort somewhere else. I wasn't expecting anything but to sleep in an embrace, but one thing led to another.

Now, my current boyfriend knows all about this. I definitely WILL NOT cheat on him. We've waited a year to be together and we don't plan to mess it up. But is it possible that my past (regarding my own action) is feeding my paranoia?

I had a talk with my boyfriend about this as well. He was very honest with me and said: "If I had any doubt that you would cheat on me, I wouldnn't have asked you out." He puts so much faith and trust in me. He doesn't doubt my loyalty. So, what does that signify?