How do I get my ex gf/bf to talk to me again?

It's a year since she left me, she was my Best friend and then she wanted to be my girlfriend, and we stayed together for three years.

I was really hurt when it ended, and I felt betrayed because she went to Japon just after that, and that was something we swore to do together. She could have waited a bit.

I couldn't talk to her utilise she got back, but when I tried, she ignored me. And now, she erased me from all of her social network, supposedly because of my behavior, because I tried to overcome my shyness around girls, by trying to talk to girls.

I sent her a letter, and she never answered. Her roomate told me to stop sending message (I send like three or four message over the whole year).

I really don't understand why she reject me like that, I don't understand what I might have done either.

If you​ have even the wildest idea, feel free to share it !
How do I get my ex gf/bf to talk to me again?
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