It can be seen that your boyfriend has made such a request to you, which shows that you and your boyfriend have deep feelings, but after all, your relationship with your boyfriend has not yet become a formal relationship between husband and wife, so it is still very dangerous to involve a lot of money.
First, lending money to your boyfriend means you have to bear the risk of losing everything! Although it is common for men and women to spend money for each other when they are in love, even men and women friends must think carefully about borrowing money. Because the relationship between boyfriend and girlfriend is not too strong after all, once you lend money to each other, you will always worry!
Second, as a girlfriend, there is no need to borrow money from her boyfriend's brother! Of course, the ultimate goal of being a boyfriend and girlfriend is to become a real husband and wife, and once you become a real husband and wife, your boyfriend's brother will also become your own relative, but now you and your boyfriend are not legally married, so you have no responsibility and obligation to lend money to your boyfriend's brother.
Third, you have the absolute right to decide the use of your own money! Although the money you put into the fund is spare money that you don't need for the time being, it doesn't mean you have to lend it to others. If your boyfriend needs your help badly, you can also choose to lend some money to your boyfriend, but you shouldn't lend all your money to your boyfriend.
Borrowing money is a great test of interpersonal skills. If you lend money to someone who doesn't want to pay it back, your money will suffer some losses. Therefore, before we borrow money, we should be mentally prepared. At the same time, you should also consider whether your relationship with your boyfriend can remain stable all the time, because only in this way can you get your money back when your relationship with your boyfriend breaks down.