Normal, Maybe he is in man's month period mood.

But it is irrelevant to his background, I am from the rural,and most of my classmates are from the big city, but most of them are very mean in money even their family are a lot richer than mine.

You can do it behind him if you want to buy something for your sister, you earn money, that is the key, then everything will be fine. As to friends, you can talk to him directly. If he really dislike it, then keep this to yourself, you and your son can visit your friend. Why bother him?