Bunny, good on you if you've decided to end this - it certainly doesn't sound as if he had any real emotional investment sorry to say, and certainly showed no responsibility as he should have done.
Hope you notice how much better off you'll suddenly feel now Hotel Bunny has shut its doors, but regardless of that, please do NOT let him off the hook in regards to child maintenance for your youngest. It is what your child is entitled to and has nothing to do with you being any sort of money grabbing bitch - if you were, you wouldn't have been subbing him and his other child all this time. Even if you're able to manage financially without his contribution do please still pursue this for your child's sake - there's no law which says you have to spend it now, but it could be saved for their future instead.
If he won't agree voluntarily to a sum which you believe to be fair based on his income (this is possible if both parties are honest and communicative and trustworthy - I had a voluntary arrangement with my ex for 14 years) then you must approach the CSA or whatever it is they're called these days. I suspect unfortunately that given his track record he'll either make you jump through hoops to get what is your child's right, or, he'll offer you some paltry sum in the hope you'll back off. Please don't let him do any such thing, and certainly don't feel guilty or anything if he starts to prattle on about how any arrangement with you will affect his older child. Fact is, he now has 2 children, not one, and he has an equal responsibility to them both - don't let anyone persuade you otherwise. You can check what your child is entitled to on the CSA site, which will also take into account his older child.
I also hope he mans up and continues to see his youngest despite the split. He appears to have a good relationship with his older child so he's not totally dreadful - I hope.
Sorry you've had the predictable responses from some on here who love to kick someone when they're already down. Talk about shutting the stable door after the horse has bolted etc (what is the bloody point in asking someone why they had a baby when the baby is already here ?? ..... an 'ill-advised' decision, in someone else's opinion, doesn't alter the fact your ex has responsibilities and was taking you for granted) and as for petty remarks about grammar, good god, do people have nothing better to do ?!
Wish you the best of luck - I know you'll feel odd, and disappointed, and sad etc but also bet you'll feel like a big weight's been lifted from you. It's horrid to live in an atmosphere where your so-called partner treats you with contempt and clearly 'isn't into you'. It's much better to be 'alone' on your own, than to be 'alone' within a 'relationship', which I think is what you were really.
(As for salmon, a moot point now, but I was going to suggest you bought a tin of salmon Whiskas (or Aldi value cat food for that matter) and gave that to him as a parting gift!)