I think Id be tempted to be cold and practical.
As others have said, if you are seperated but in same house, you may be entitled to some benefits now, even if you are working/studying.
Sit down with him and say that you need to sort out parenting jobs - so ensure he cant swan off on nights that you are working, leaving you in the shit, and perhaps some 'free time' for you to be out 'enjoying yourself' (you dont need to be doing it, but it needs to be factored in)
explain that from now on, as you are no longer his wife, that you will be considering him as a flatmate, so he is responsible for his own cooking/laundry/shopping, plus 50% of all housework - perhaps he might like to divvy the jobs up now?
equally he needs to ensure that school uniforms / homework etc is his responsibility for days/ nights that he is looking after DS, because going forward thats going to kick in once you are living in seperate places, so he needs to get on board all the mental load regarding school/appointments/parents evenings/parties etc, as you wont be providing that information any more. He also needs to have a think about how its going to work going forwards - is he looking at 50-50 child custody - can he do that practically - or is he expecting you to do the majority, in which case he is going to need to consider maintanance. It also allows you time to plan how to cover your nights - do you have family near? will you need to look for a different job / change work patterns. Speak to your boss and see whats feasible.
Its not to 'punish' him, but to ensure a smooth transition for your child, and to enable you both to move forward to an amicable separation. Its kind of stuff they really would like you to have sorted out anyway before a divorce is granted.