One past memory could throw us into deep sadness and depression. I suggest to forget him, and move on. He hurt you, and probably blocking him from contacting you and from all social media is a good idea. Facebook shows a tiny good slice of the reality. You feel this way now and I understand that. We find it hard to imagine ourselves in better situations when we are sad or depressed. But in the future, and in retrospect, probably you will say you were wrong.