Most Helpful Guy
Who cares really, that should be your stance. He made you his ex, therefore your life is no longer his business. Just remind him of that. Remind him that he made his decision and therefore you are not answerable to him anymore. He should focus on his own life now, just as you are doing.
Most Helpful Girl
Because most people after a relationship is over is frustrated that their ex has moved on, but they still haven't, even if they didn't really love them. They might be jealous of the other person for being able to find happiness.