This is my opinion:
As Dan and Jennifer say, communication is the key to a good relationship. Tell her how you feel!
Also, did you say your ex girlfriend and best friend had been together before? maybe she never stopped having feelings for him.
Oh, and DON'T DRINK ANY MORE!!!!
It sounds like that is partly what got you into that mess. It's a well known story-guy drinks, loses all chance in current relationship.
If you want any chance, stop drinking. I got through a similar crisis without drinking. indulge your creativity (write books, write music, write programmes, listen to music...)
Finally, before you tell your ex, the way to get out of your current relationship:
Ah, now this is tough. Try the anti-depressing things i mentioned earlier togeher. Don't get too close, but don't drop too many hints that you're leaving. Slowly distance yourself whilst indulging creativity.
And, (really 'finally' this time), your english is great!