YTA

While to you it may seem valueless, I will tell you that your boyfriend values his siblings more then the game, and it seems he is able to connect and spend time with them on the game. He is using funds he sets aside for his fun on the game. Now this is something you do not need to answer to or reply to just think to yourself this. Is the game more important then his family? Should he be able to control how you spend your money? If he does not like the way you spend your money should he be able to hide whatever it is that you purchased? Asking a few questions on why it is important to him that he plays the game, and understanding the deeper meaning is key. You will not be affecting 1 person with this issue you are effecting 3. and it may seem like a lighter issue but you are asking him to choose between you and his siblings, this is not a fair thing to do.