First off, my condolences about your friend, that must be hard for you especaily since you were in the car.
Secondly, if you think you are drinking too much, talk with someone around you, if you can get someone else involved they will be more likely to find stuff you can do, or just hang out with you, to curb your drinking.
Third, yes it sucks to lose someone you were that close too. But maybe just take a month apart and see if you still feel the same way about her after that period of time. If so then try to do everything in your power to get back together with her.