He should absolutely be paying half unless he could have him on some of the days so you don't have to send your child in as much. Don't think he'll find this unreasonable at all. Hope you're okay xx
Sorry to hear that you’re in this situation 😢 Absolutely he should be paying some form of child maintenance - either the two of you can agree an amount amicably or you can use the child maintenance service Depending on your income and any savings and investments you may become eligible for Universal Credit once your partner moves out - worth investigating.
Why don't you think you can have that conversation? Why would it be on you to pay for all the childcare when it's his child too?