I'd kill her so she can never be happy again.
I jest, it's a tough one as everyone deals with it differently. I have been in the situation you have been in before and it is hard. I split up over Christmas and for a few months I thought she would come to her senses and get back with me... when i found out she was dating someone else I felt lower then ever. I got drunk, texted her some hurtful things and she responded by saying it would be for the best if we cut contact completely (we had kept some contact prior - odd text, email, etc)
The complete lack of contact was a godsend as I moved on with life and started dating again. You have to accept she doesn't want to be with you anymore. Be grateful of the good times you had together and the memories, you will always have them but you need to look forward and not back. Do you think if she has moved on and is enjoying life and she knows you are getting drunk and high at home she is going to regret her decision? Hardly.
What you need to do is stop drinking heavily and doing the drugs and get out with your mates for meals and social events. Surround yourself with good people and you won't mope so much. Keep in there pal, it will get easier with time
Thanks Xela mate I just can't wait for 2015. Fresh start and all.