<human>: We dated for 3 years in high school and into my first year of college. I broke up with her my freshman year for no reason. I called her(we'll call her Julie) up out of the blue before spring semester was out and told her I didn't want to be in a relationship anymore. I told myself being single would be awesome and college would be more fun.

Fast forward to senior year, I finally found my second girlfriend. It lasted 9 months and I finally broke it off because both her and my friends kept insisting we were no good for each other (she was an alcoholic who started fights every weekend and I played Mr nice guy and forgave her every morning). 

Since the break up all I can think about is Julie. I've never felt this hurt/lonely in my life. I know that I made a mistake in leaving her and that I must have hurt her and made her feel just as lonely as I'm feeling now. 

She currently has a boyfriend and is a senior in college. They have been dating for about a year. I know I don't deserve her back, I know she has a right to never trust me again. I know she has moved on and has found another man.

also - before I started dating my second girlfriend I  called her while she was with her boyfriend (of only 2 months then) and he answered, threatened me blah blah blah. Anyways I facebook messaged her the next day to apologize and she said she didn't care at all and told me she would never hate me... so i guess i have that going for me. 

So, Reddit, Give me some ideas on what to do. I'm planning on sending her a letter soon. A much more detailed version than this explaining myself and telling her how i feel. I know this might be crazy, could back fire, could never even be opened by her, but I need help. So I leave it to you, my people, any suggestions?

Can you condense the text into three sentences or less?
<bot>: I(22M) broke up with my high school sweetheart(21f) three years ago, She is with another man and I need to win her back. How can I pull this off?