How to deal with the fact that someone who I trusted the most, ended up hurting me the most?

So i had a best friend in high school, and i had known her for two years before we began dating.
We were very a strong couple but things became tough because she moved to a new school and after high school moved to Japan to pursue BBA. By then we were dating for 2 and a half years. But she didn't want to continue and broke up with me giving long distance as the reason.
We kept in touch though and she started dating other people in Japan but told all our common friends to keep that from me so that i won't stop talking to her!!
And after two years, once when she came home we met and she told me that she had made a big mistake and she was miserable and wanted to date me again. Apparently her other boyfriends were jerks and one had even physically abused her.
And since i was still in love with her, I said yes. She then took one semester in Australia and and began partying everyday. she stopped texting and calling. She wouldn't even reply if i told her that i love her. And then she told me that she had her exams coming up and would be busy for some time, I told her to text once she was done. But she never did and after a while i get a text from her saying that she was back home for vacation. I figured maybe she was maybe in stress and so forgot to tell me so i kept quiet. But then i found out that on the way back she had a layover in Singapore and gone on a date with one of the guys from back home who happened to be in Singapore too.
She didn't text or call me even though she was home.
When i confronted her, she told me that she doesn't have the same feelings for me as she did before.
And also somehow managed to convince me that it was all my fault and i had to be more attentive in the relationship. I just feel like she used me because she was feeling low in life.
And the fact that she used to be my best friend doesn't help either. I feel like if someone i trusted more than anyone could do that , then how do i trust anyone. I feel like i can't date anybody ever again.
How to deal with the fact that someone who I trusted the most, ended up hurting me the most?
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