Y is he acting like this??? ?

So to make a long story short I'm 18 a Nanny of 3, a preschool teacher and more importantly a Aunt of 6 awsome kids that I treat as mine.. My boyfriend has suddenly gotten mad bc I spend a lot of money on my kids at school,nanny and esp my nicest and nephews but I don't think its a big deal bc I pay for most of [our things) save some money,and still have more money than he has.... I just don't understand y he suddenly cares where MY money goes!