If she suddenly broke up w/ you for no reason at all... I'm guessing she cheated and is w/ someone else, feels guilty, and doesn't want you angry at her. Otherwise they'll just give you some it's not you, it's me platitude.
Anway, I'm sorry you feel this way. I've been there, and it genuinely sucks a lot. The good news, it gets better. The bad news, it takes time and you won't feel like you're getting better until you finally look back and realize you do.
As for how to get her out of your head? Time, friends, distractions, coping mechanisms. Take a vacation, go find new things to do that are not associated w/ her, put a 1 month moratorium on anything that is related to her. Don't accept phone calls from her, don't talk to her, take all her gifts, box them up, put them away until you can deal with rationally deciding what to do with them. If you do find out she's done wrong by you, take items, burn them or something. It's silly, but cathartic.
Go take up martial arts or something that requires you to hyper focus. Get mad, get angry, punch a punching bag, get the bad energy out of your body. Crying, sadness, depression. All pain and bad energy directed inwards. You only end up hurting yourself.
Oh, and while this doesn't help. You'll probably find someone far better.
Keep your chin up, stick to the high road, and you'll feel better and come out of this in a positive light in the eyes of others... Like potential women to date.
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."