I was in a place like yours not so long ago. It feels like a lifetime ago now, but in reality it was only two years. Just goes to show that time is a great healer for these sorts of things. I was kept over night in hospital after a suicide attempt, and I broke up with my ex, who was also long distance. I was a mess for a while, thinking that if I couldn't be enough to stay with them then I couldn't be the man that I am (or something like that, I can't remember the details of what was going on in my head). You can pull through this too, and we're here to support you however we can.
Your ex having a problem with your body is her problem and nothing more. She was likely saying hurtful stuff because she was ignorant, a lot of people just don't understand, or haven't had the exposure to trans people before. Do not blame yourself for the way she treated you, because focussing on your body and making you take the blame for everything to stay together isn't healthy in a relationship. It's a two way thing, particularly long distance.
Parents are hard. It takes time for them to fully adjust to the idea of their "daughter" really being their son, and often can't understand why being a tomboy isn't enough. That she's willing to talk to the Pride Center is a good step, it shows that she's not just brushing it under the carpet. You've had your whole lifetime to come to this realisation, and to research stuff, and she's only had a month. Educate her, and try to show her that this isn't just an extreme case of being a tomboy. A lot of parents come around when they realise that their children are happier, and that's all that parents really want.
I know for certain that I'm glad I never did anything too drastic back then, and you will be too. At the very least, think about whether you want to be remembered by your gravestone as your birthname, or by who you really are. Give yourself a chance to live your life as yourself, not as a pretense of a girl.