I just got out of an ugly relationship myself...i thought i was going to marry the girl and she fucked me over....hardcore, i can't even begin to describe the level of manipulation and deceit. I sacrified alot of my life for her, and felt like i was left with nothing.
that being said, it's been a month and i'm pretty happy with my life.
best thing to do, is not regret the past...learn from your mistakes. It probably didn't work out for various reasons. Maybe she wasn't the right person, maybe you weren't in the right place in your life...Point is, don't dwell in a pile of shit. First few days you will feel like absolute ass and you won't want to do anything...and the pain will be there for a long time to an extent, especially if it was a long and serious relationship. But you can't change what happened...all you can do is realize what went wrong, and either don't pick a similar person or correct your mistakes.
What you NEED to do now...is focus on bettering yourself. Have fun in your life. Work harder, get in the gym more, spend more times with friends and family (they're ultra important in a time like this). The more you focus on yourself, the happier you will be. I went on a fucking spree and it temporarily helped, but the more girls and people you meet the better you will feel. The first time i fucked another girl besides my ex, it lifted a huge weight off my shoulders. My confidence and swagger started coming back and i realized why a girl should be with me. Don't get wreckless and start doing alot of drugs and drinking, but have fun....get your shit straight (if it's already straight, make it better). That's how you recover.....you will think about her, no question, but limit your thoughts and don't obsess... and grow and learn from this experience. 95% of the time, way after the fact...you realize you're better off (unless it's a divorce situation and kids are involved, that makes things much more difficult). If that's not the case, consider yourself LUCKY!! You won't be able to think that now, but you will over time
See a therapist if you can afford it and if you feel that you're that broken up about it....
Bottom line is, if you're not valuing yourself, no one else will
ALSO...limit contact with her or cut her off completely. The more you speak to her or try to talk to her, the more the pain will continue to resonate. It will almost never go away if you still talk to her. Everytime you speak or communicate with her, all those emotions you're feeling right now will engulf you. If you DO want to speak to her again, wait till the pain heals...which will be awhile. Dude, i just saw you're 20 years old.....you don't know what the fuck the love of your life is at that age!!! Take it from me, i fucked up by being a serious and commited relationship at a young age, and now i'm making up for lost time. It stunts your personal growth!! Have fun for a few years, get your shit straight and the right girl will pop up