Hi Shmmeee. I can only imagine what you're going through now, and like everyone else here I wish you weren't suffering through it. For my money emotional pain is in some ways harder to deal with than physical pain because it can seem like there's no end in sight.
However, the good news is that you will get through it. Much as it pains me to say it, you're a decent, intelligent, resouceful bloke, and you've got reserves of strength that you're not even aware of yet. It's a shit way to find out about them, but trust me, they're there.
My honest advice, for what it's worth, is to look after yourself a bit. Don't internalise it all and start blaming yourself, there's no point to that and (imho) it's as damaging to your mental health as trying to pull together reasons for it. Deal with what's directly in front of you and try really, really hard to avoid peering too far into the future - it's honestly not as bleak as it seems right now but it will take time to see that no matter what anyone here tells you.
Remember that you've got mates here and in real life that you can talk to about it, and similarly that you can ask not to talk about it if you're not in the mood. Use 'em, it's what they're there for! And treat yourself to something that will cheer you up a bit - DVD, book, computer game, whatever. Something that you can lose yourself in for a while.
For me when I was going through a rough patch, running and physical exercise helped - and even now I still hide away and play crappy on-line games on
Games at Miniclip.com - Play Free Online Games if I feel myself sinking down a bit. We're all different so this may not work for you, but there will be something that will. Personally, I'd advise avoiding the football if you need cheering up, but a good rant at Fisher/SISU/the ref/the goalie might be therapeutic - it seems to help sometimes.