Its so hard to find the motivation to help yourself when you feel like this. I know it may sound pointless but the above advice really is sound. Try to talk to someone if you can - if the samaritans have a stigma that puts you off (they really are a great support and you should try them if you can) then try ringing MIND the mental health charity and they may be able to help and advise you.
The place you are in will be one sided and your arguements to 'stay or go' will be unbalanced and unrealistic. If nothing else, talking to someone impartial will add a more balanced view of where you really are with your life. Alcohol will not help this process and I know it sounds 'preachy' but try to cut it down or even out completely if you can.
Please dont feel alone. I myself was at the end of my teather just 1 month ago. I had a plan, and I had even gone to the trouble of gathering tools together so that when i got the courage I could just get it over with quickly. I took time to talk to people even when i least felt like it and I now have a more balanced view of things. I still struggle and its not easy, but I can see what im fighting for now, I realise Im not alone in how I feel and it makes a huge difference.
Hang in there and keep posting.