All this "ooh he just doesn't see how much things cost" bollocks.
Love, show him. Sit down with an excel spreadsheet. Show him what you currently pay for everything. Show him how much of it he will be responsible for when he moves in with you. It is impossible to argue with black and white figure in front of your eyes.
On £38k he will have a handsome salary. From that salary he currently pays very little out on living costs. He has ENORMOUS amounts of disposable income (and also enormous amounts of debt
). He won't have that same money when you live together, because quite rightly you'll be sharing costs.
If you want to stay with him lay some conditions out of your own: You won't even consider discussing it again until he is debt free and has remained so for 12 months. By this point the employment aspect will be moot because you'll be doing what you want work-wise, but just in case, make clear that your employment choices will not be dictated by him. If you are to live together as a family you behave as a family and that includes splitting all costs for the family in the way you both decide works best. And such splitting of costs will include his child maintenance payments, plus all childcare costs for the family he is asking to move in with.
You also need to have a discussion on how you would raise the children together, how you would discipline the children together, how you would save for children's future's together, how you would plan your lives around your employment (would he expect his career to come before yours, for example? What if one of you wants to change career/go back to uni/go part time?), what your priorities in life in general are. I don't see that you've done any of that. Well, I see that they've sort of come up, and they show you have wildly different priorities, and yet for some reason you're both ignoring this.
Don't tie yourself down to someone who wants to change you while not changing anything themselves.