An EX BF who disappeared on me without a goodbye tries to re-enter my world again. What to do?

We dated for about 6 months, we really were the couple all would be jealous of blah blah blah you know the story. One day, he decided to cut all communications with me. He changed his phone number, he deleted all his profiles on social networks where we were friends and re-created new ones. Blocked me from Skype, MSN, Yahoo.......everything! And disappeared without a single word. A few days ago he unblocked me from Skype and started appearing online very often.(btw, he has 2 contacts on his lists, one of them is me). I know that most of you would say that I should forget about him and move on but I really loved him back then. I still do. I do not have any intention of getting back together with him but what should I do now? Appear online to him or not? Talk back in case he starts up a conversation? Act casually? What would you do? Thank you all in advance!