You begrudge a child, your dps niece a warm home, now, do you? And you begrudge the woman who has raised your boyfriend means to better her career prospects?
I think you need to recognize that his sister has been in his life a lot longer than you have been in his life. She has also cared for HIM.
You also need to recognize that although 2500 is a lot of money over three months, they have been spent sensibly. We paid 2k to replace our boiler, 6 years ago. Laptops are not cheap either. He is providing her with means to study, so she can earn an income of her own.
You already have an income, don't you?
But I bet it bugs you, because in YOUR mind, the money would be better spent on you...
I honestly think you come across as a money grabbing gold digger. You dont recognize that this is an honourable man with care and empathy for his family, instead you are miffed that he does not spend the money on YOU.
On 18 and 42k, you don't really NEED to save for a baby. But a child that is already born, needs to stay warm. Shame that you begrudge this child a warm home.
I honestly think you are living under a bridge, because nobody could be so callous...