Here is my take on your situation... the post to me says much more about you than him. Who knows why he is doing what he is doing, could be a billion reasons... the rush of new love, instant gratification, boredom, etc.
I watch my dearest and closest friends get in relationships that I know are bad for them and just sit by. Because it is their life to live and the only way some people learn is through mistakes. If they ask me for advice, I give I never presume I know better than they do about how to live their life.
So as for you, you started out saying that you had a relationship with this man, not "I have this friend that...". You talked about the relationship, the push/pull, how you were hurt. So you settled for a friendship. You still have feelings for him and that is evident. If so, it must be painful to see him involved with others on a deeper level. If it weren't, maybe cyranoaks response wouldn't have triggered a reaction. This is a sensitive subject for you.
What most are saying is it is about looking at yourself and focusing on your life and making yourself happy. If what he is doing is causing you pain or frustration then maybe there are deeper motives in wanting to 'keep track' of his love life.
Maybe because I just sit and watch my friends make the same mistakes over and over but I still support them and unless the guy is abusive or a con-artist, I basically do mind my own business. I wouldn't want them to analyze my love life (heaven forbid) or get preoccupied with it, would you?
Hope some of this helps.