Lame I know, but smile sweetly when you see him, ask how his mum is (like you care!!), tell him how well you are doing.... that you are off to the cinema tonight, have been down the gym, going for a meal, etc etc, possibly drop in the convo that he is looking tired, is he eating properly, etc etc (again, not at all concerned but will scarethe sh*t out of him).
It will completely throw him because he will expect you to extract revenge. Bide your time, what goes around comes around. You wil have an ultimate opprtunity to drop a load on him and it may not be for years to come but it will be worth it ;-) Best of luck x x