When you go to work, talk to your boss privately, say you are in the middle of ending your relationship and might need to take some leave to sort this out as you'll be homeless with a small child. You can ask them to keep it private beyond that, it doesn't need to be public knowledge until you're ready to tell people.
Do you have any savings to yourself? Could you afford to rent somewhere and live on your income near enough to work? What about your DS, do you have childcare arrangements that rely on your 'D'P to do pick up/drop off? If not, get sorted about moving. There's help out there for single parents and it doesn't matter how 'stingy' he is, he will have to pay maintenance. (CSA is easy to contact).
To me, it sounds like your DP doesn't like you, but he recognises you and your DS are a package, he's putting up with you to keep his DS under his roof, but doesn't actually feel the need to hide the fact he doesn't want you. I don't know any couple who've stayed together for the DCs actually make it work in the long term, and in the short term, most are at least polite (if cold), he's not even bothering to do that.
Take some time off work, get your own flat sorted (you can always apply for a council property, but if you can afford to privately rent, that would be a lot quicker, most are empty when advertised so you could move within a couple of weeks). Tell tosspot you're leaving, if he's not civil between now and you going, go stay at your mums and tell work you need more time.