I have been with my fiance nearly two years. I have always trusted him and thought the world of him. We are buying our first home together shortly and getting married later this year. I did something I have never done before yesterday: I went through his text messages. He never deletes his texts and I saw one from when we first started dating (it was about a month after we became "official). He was telling this girl that he wanted to hang out and she agreed but she knew he had a girlfriend (me). He told her that he was waiting to see me to break up with me. They never hung out from what I can see from texts between them, and he obviously never broke up with me. Regardless I am extremely hurt and confused. I feel I brought it upon myself since I looked, but I feel that was something I deserved to know. Even though it was nearly two years ago, it is still upsetting me and making me question if he really loves me and wants to be with me. Is this all in my head? Am I being super paranoid? I am trying to forgive and let it go but it is extremely hard.
Have you never changed your mind? Have you not gone through periods where you've questioned whether you are making the right decision? (Such as you are going through right now?)
Given the timing it appears that he went through a moment when he realized he was about to make a permanent decision and he wasn't completely certain. Like many people he decided to compare, but in the process realized that what he had was too good to let go. A month later he asked you to marry him. I suspect that he came to his decision just after the texts you found.
It was two years ago. Clearly once he made his final decision, he stuck to it; otherwise, you would be complaining about all the other texts that you found. Thus, yes, you are being overly paranoid. Look at what is, not how a person got to this point. "You will know them by their fruits. Do men gather grapes from thornbushes or figs from thistles? Even so, every good tree bears good fruit, but a bad tree bears bad fruit. A good tree cannot bear bad fruit, nor can a bad tree bear good fruit" (Matthew 7:16-18). When in doubt, look at what a person does. It is usually a clear indication of who they are inside.