Most Helpful Guy
You're only going to reaffirm his decision when he sees you pettily trying to make him jealous.6
Most Helpful Girl
You don't. Doing something like that will 99% of the time not make him regret choosing someone else over you. So in the end you'll still be alone, on top of looking and feeling like an idiot.
The best way to get redemption if you insist on getting that is showing him that you're fine, if not better, without him by your side.1