Ignore them then. Right now the plan is working, their in your head

The only way to deal with that shit is to completely blank it. Carry on with your life and just blot it out. It's the worst thing you can do to people who like to play games. What does it matter if she's screwing someone else? You two are done so it's no longer your Circus or your monkeys. Go find yourself a good rebound and move on. It'll piss her off more than anything else you could do. If, on the slight off chance, you're reading into things that aren't actually there, this approach also works. Go forth, get pissed, get laid and get on with your life. Best revenge out there.

So move on and find someone new. That way you can tell her you have a SO and need to give them your attention. Let her learn from you and finish moving on.

get better friends

Dude, just start being super excited when they bring up a new person. You know it's a game, so start playing. "I'm so excited for you, have you got any holidays lined up? I can recommend an amazing restaurant you guys should try"... etc. Once they think you want them to be with someone else, they often lose interest in torturing you.

Why do you care who they brings or dates? Just move on, don't ignore it, make it not matter to you. If they have someone great be happy for them. If they lie, well, the joke is on them