Don't feel down on yourself! If anything be proud. Hell you did a lot more than most people would and if she doesn't appreciate it, imo she is either not interested or feels like she has something better. Nothing hurts more than having your heart broke. And nothing makes you feel better than being in love. If you know she is no longer interested try getting to know the new girl better. You may think now that she isn't as pretty as B, but once you get to know her better you may find she has more in common with you and is a better fit. I am not saying jump into a "rebound" relationship, and, like I said before whatever you do don't hurt her if things turn around with B. If B does show interest after you begin a new relationship it will show she might just be jealous or still mad and only wants to hurt you.
The ladies on here know more about other ladies than I do, so take my thoughts with a grain of salt. I've been used by women and chased them just like you, only to find they didn't want me. They just wanted what I had because they knew I'd never turn my back on them. Looking back I would have been better off turning my back on them as soon as they did it to me. Just mho. Whatever happens I hope it works out you. I wish you nothing but the best, just like all the others here.