Why don't friends ever last?

I'm the introvert. The "quiet boring girl" according to everybody at school. I'm never happy. Its like whenever something good happens to me god just says oh sophies not worthy, and then my life gets bad again. Ive never had more then 1 friend at a time. And every single one of those friends left me. Every single frriend I get leaves me. This year I thought I finally had a good friend. She accepted me for me. She saw who I really am and didnt leave me. I guess it was stupid of me to think she would stay. Last month I found out she's bi-sexual and yesterday she texted me that she has a crush on me. I'm straight. And now we're really awkward when we talk. And she said that if we're this way when school starts that she won't talk to me but if I want to talk to her that I could but only a little bit. What a friend right (sarcasticly). She's not quiet like me. I know this school year is another one I'm gonna spend completely alone.