Whay do I have so many chance meetings with him?

This guy that I went out with "dumped" me without contacting me. I also found that while I was patiently waiting to hear from him he was flirting with the girl I work with. So, I found out about it and I got mad, and told him that I would no longer be communicating with him. The problem is that I work across the street from him and I go to the same University as he does. He never comes around me and I never go around him that is on purpose. It has been harder for me to move on, because I really liked him, and when he dumped me without an explanation it hurt even more. Occasionally he and run into each other, and the past couple times that this has happened, he basically sees me and immediately goes to another side of the room, and the other time he literally "ran" away from me. However, the other day, a chance meeting happened again, and he was a little more mature about it. He actually said, hi and asked, "how are you" I decided to just be nice and I gave him a friendly smile, he then chuckled a little, and it had a cheery sound to it. What am I supposed to think?