Years ago, when I went to see a counsellor, they talked to me about how when we've been part of a couple, our whole self-worth and what we think of ourselves is so bound up with what the other half thinks.
They may be an utter wanker, but it takes a while for the dust to settle and for us to see it.
I know it's hard, but never mind about his girlfriend. Pity her. You are free from this callous man now (who also sounds a bit dramatic and pompous). Your life is on the up. You may feel really, really, really low now. But if you could fast forward your life a year and take a glimpse, I'm sure you would feel relief, freedom, optimism.
The hardest part is getting through the next 365 days of daily routine to GET to that point where you realise, oh my GOD! I am happy again!
So for now, focus on the small things you always enjoy doing, relationship or no relationship! Cup of tea and reading the paper?? Jog 'round the park? The endorphins released are very GOOD natural anti-depressants. Pushing yourself physcially can really make you feel strong mentally. it's how I've coped with a lot of sh1t and anger myself.
Good luck.