Gavin,
bigmamma has given you some excellent advice, my advice is to take it, and as you can see, the majority on here are for you, and want you to come through this, it won't happen tomorrow, but starting to talk about it is a beginning.
Right now, your at rock bottom, things can only get better, you've taken the first step by coming on here with it, now for the second, the Samaritans are anonymous, which is good, dial 141 before you ring, and your number is hidden, then the docs, they are trained to listen.