Why did he stop talking and dealing with me?

Steel hit it right on the head. I had someone that I kinda did that to (much to my shame) and yeah I acted just like that. Let him know that it's over and that you're moving on. Eventually, you'll fall outta his sights and things will be "normal again. Might wanna try putting some distance between you and him though so he can hopefully find someone else to be the source of his affection.

Guys want what they cannot have. Once he saw that you and him were a thing, he probably gave up trying expecting you'd still be there. But when you broke it off, all those feelings of familiarity he had with you came rushing back.

Now that he sees you with other guys he's jealous, and wants to be the only guy in your sights again. Now, knowing what he's done already to you, are you willing to take that chance again?

He was trying to play the game, and he went about it wrong. Now he is trying to get another chance at it.

Don't get hung up on the why, and instead feel flattered that you've grown past that jerk. There's absolutely no reason you need to sit around feeling rejected when it's obvious there are other men interested in you.

You keep up with your life, and I can guarantee this former boyfriend will be begging forgiveness with reasons on why he ended things in such a rude way. You'll have your answer and he'll have his right hand.

Ask him. Just ask him what kind of game he is playing? Tell him you don't like it.