Was I his fall-back girl?

We've been together for a year. Recently he left his messaging program logged on my computer. Bored, curious and totally unjustified, I decided to read through his past instant message conversations from around the time we got together to see if he talked to his friends about me a lot. He didn't....in fact most of the friends he talked to were other girls....long late into the night conversations with a lot of different girls. When he talked to his guy friends, he mentioned other girls he liked, but never me. They didn't know I existed until they came to visit and we all hung out and his roommate hinted to them that he liked me. He even had a conversation with a friend about a girl he liked, a girl we are still friends with and hang out with often...it seemed like he asked me out because he really wanted a girlfriend and I was around a lot. Is this something I should be concerned about? Before you say it, I know I was wrong in reading through the convos...I really thought I'd find something cute in conversations with his friends about me, but instead I got conversations with his friends about other girls and conversations with other girls (none with me, I didn't even know he had instant messaging back then). He actually did mention me once to a friend, but only as "an associate who might be able to drive us somewhere." What the hell is going on? It seemed like he liked me, but after reading these conversations I feel stupid and insignificant.

And one more time, I KNOW I was WRONG to read the conversations.

Should I try and bring this up to him, or should I let all of this go and try and forget it?