Ex boyfriend trouble!?

First of all yes he's on the rebound, because this will take his mind off the pain, so he isn't really that happy underneath it all, it's just a distraction to take him away from how he really feels. Secondly, obviously you'll be upset seeing this if you were with him for 3 years, you shared a lot, you only want him now because you can't have him, if he was single and weeping into his pillow every night I doubt you would have changed your mind about wanting him back. Thirdly, yes he wants nothing to do with you because you broke his heart and any contact with you will remind him of that pain. So yeah this is all pretty standard break up shenanigans, don't worry too much about it, it'll pass. But don't get upset about him apparently moving on and being happy so quickly, he isn't really, just like when people's pet dog dies, some of them go out and buy a new dog straight away to try and fill the void, it's just their way of not dealing with the pain. And because of this sadly instead of dealing with it they repress it down by distracting themselves with a new dog or a new relationship or whatever, and they will carry that pain subconsciously instead of releasing it as it happens.