How do I handle my ex-girlfriend treating me this way..?

From the one I see it, it seems like she was just using you the entire time. Obviously she hadn't gotten over her previously bf (for whatever reasons) and she probably just wanted to go out with you as an attempt to forget him. This might be hard to accept but a lot of times this happens. No offense or anything but from what I've read, she sounds like an outright b*tch. I would just move on if I were you. There are a lot of girls that would appreciate the stuff you do, like write letters and stuff, that are far better than her. I think your best option is to move on. Right now it might seem like shes the "perfect" one but one day you'll find another girl whose even better and will really like you and appreciate you back. Trying making new friends and getting out more and maybe just talk to strangers. Best of luck