You're just a pubescent kid, you think she's cute and she gets your hear pounding. That's all. But you've got to realize maybe she just doesn't like you, or maybe she's out of your league and doesn't want to be seen around with you, or it could be that's she's more considerate to her friend and her ex than you are. Have you thought about how that might effect other people? I suggest you move on from your ex and this girl and find someone nice, but yet, obtainable, for you at least.
You´re an asshat, I don't know if you are trolling or not, but you´re not helping him. He´s probably young and he´ll get over her and the next one. Besides there are many fish in the sea, just have to find a tasty one.