You cut your losses because it wasn't working for you. You tried it again, and it still didn't work for you. While it's normal to feel hurt, do you really think he is going to treat this new girl in a way that is much different from how he treated you? Yes, people can change, but it takes A LOT of work and effort. He may change a little bit, he may change only until he gets comfortable, but he may not change at all. Don't think about it as "why her and not me," the truth is, he wasn't enough for you. You deserve to be treated better than that, and if you expect more from people, you get more, but it's never easy in the process.