Thank you all for the messages.

Some time has now passed and things went back to normal between me and my bf, I decided there was no point in blaming him for the way his brother is acting. The brother seems to be an utter idiot, that's all I can say.

It's true that I should learn more about iranian customs, and I will do, I'm also starting to learn their language bit by bit. My bf is not a muslim but a protestant, and he's heavily opposed to Koran and all the 'man world' laws. When he was in Iran he used to drink alcohol (socially), which is strictly forbidden, and he loves the pork chops I make.
But the fact is his brother is much older than my bf and he holds a kind of power through that.
My bf told him that he is planning on getting married to me - all the brother said was 'it's your life, do what you want'