Why is he acting this way?

He's my best friend and we've been through everything. We use to date but now we have this weird off and on vibe friendship. Its as if he's afraid to commit, but he wants everything else a relationship includes without a title. I suggest we see other people and he says i guess, like he's irritated I'm talking to him. In the end its an heated argument with him stating here we go again and I suggest its not we and he says yeah your right its you. Since then I cut off all contact with him in two months. I noticed on his social media he posted I guess shes moved on. Weeks later I contacted him but kept it short. He seemed happy to talk with me, but we never talked about what happened. Should I just leave it alone and move on?