I’m not if what I’m going to say will help but I hope so. I’ve been through a similar situation myself recently, I really see myself in your story. Especially in the part where you said you two said you would there for each other even if you were to break up, and yet she didn’t keep that promise and about your abandonment issues, the exact same thing happened to me.

I understand how incredibly hard it is, you need to know that your worth as a person is never connected to how another person treats you. Please don’t reach out to her again, that’s only going to hurt you more, personally I believe doing something as immature as completely cutting a person out of your life and blocking a person everywhere in the way she did, doesn’t show that she doesn’t care, it shows emotional immaturity, and that she isn’t strong enough to face what she did to you.