Norest that's a lovely poem.
OP so sorry you're going through this. As others have said, time will make things better (which I know isn't hugely helpful right now.)
Can you think of some things which you can keep yourself busy with? Meeting up with friends more often, going to the cinema (I love going on my own!), learning a language or skill you've wanted before but never had the chance, starting to swim or walk or run or dance. If you prefer your own company, starting a long series of books, or a marathon TV series, or a new computer game... anything to keep your mind and hands occupied basically, especially if it's something you haven't done because the ex wouldn't have enjoyed it.
Re you feeling so down on yourself - I fully understand this and I was fuming at myself when my last LTR ended (and like you he went off with an OW although he was a lot kinder about it than I think yours has been.) My main anger was "he's wasted my time!" and "I should have trusted my gut and finished things the previous year! I knew he was a wrong'un!" and - most especially - "Why, why did I lend him several thousand pounds that I'll never see again!?!?"
It was really hard to let go of that anger, it was like a double edged sword in that it was pointing at both of us, and I hated the feeling of the anger too. In the end I just had to write furious emails (which I didn't send) and ranting texts (ditto), and I talked the ears off my sister and several friends. I also spent more time with friends (this was actually easier as I'd moved nearer most of my friends), spent more time with my DS, started a little flower garden in my new place, threw myself into my new job, learned some PHP programming, and bought some new games. It all helped, but I'd say it was probably 4-6 months before I really felt better.
You will get there 