Would this be considered betrayal? (Read inside)

My cousin, a very close friend of mine, dated this guy a few years back. She was completely in love with him, but he was a jerk, broke her heart, and she still hasn’t fully moved on. The break up was extremely devastating for her, and he is a very painful memory. By some accident, he added me on Facebook several months after they broke up. We started talking on a regular basis. At this stage in my life, I was very lonely and insecure, he was intelligent and charming, and we developed crushes on each other. (To my cousin, I acted like I only talked to him to feed her information.) Eventually, the guy and I stopped talking, he found a serious girlfriend, and we all went our separate ways. Just today, though, I stumbled across an old AIM convo with him. I was impressed—looking back, he’s a pretty cool guy. He liked me, but there were times when I would just lash out at him and attack his character. I guess I was trying to change him to be just what I wanted, or impress him with my insight. Either way, it was a clear indication of my instability. I remember just wanting him to like me so badly. After reading, I became overwhelmed with the desire to shoot him a friendly Facebook message apologizing for being so crazy, and just see how he’s doing. I feel like now our interaction would be so much more relaxed and healthy that both of us have grown up a bit, I’m totally over the low-self-esteem phase (and I have a boyfriend now who I am happy with), and we could keep it strictly platonic. However, I know that talking to him would upset my cousin. I wouldn’t tell her about it. But at the same time, I feel like her aversion to him is irrational and there’s no reason him and I can’t exchange a few friendly messages. He actually did wish me a happy birthday a couple months ago. What do you guys think?