Should i Just leave her and walk away for good?

Alright I've been in a similar situation. So what you have to look at is this is high school now, girls think that they "love" their boyfriends and that nothing in the world matters. Is this her first boyfriend? Because that matters... a lot. One mistake you made was buying her stuff, I did that with on of my friends and it got us no where, actually it probably pushed us farther a part because she just looked at me like a money source (the difference between you and me was that I'm was broke and spending everything I had on her and I'm a tad more self indulgent) Anyway all I can suggest is sit down and talking to her, ask her to what happened to your guys friendship and tell her that you feel ignored. If she gets pissy about it leave, just walk away and let her live her own life (no matter how hard that may be) and maybe when she grows up a bit a more you can try being friends again (that's what happened to me and my friend we didn't talk for nine months) but if she wants to listen and wants to try and fix this, then work from there. Sorry this answers so long D: