Since you borrowed a credit card, it means that your brother must be in urgent need of money. So, your choice is probably correct, but your boyfriend can't understand your approach. You should try to tell his brother's predicament and his repayment ability in a certain period of time. You should coax your boyfriend, as you usually do when he is angry. You must not lose your temper, which will only destroy the feelings of two people and there will be many contradictions.
02. Get your credit card back.
If your boyfriend is really angry and you can't coax him, you have to get your credit card back. This is also a service-oriented way. Since we can't make him compromise, we have to compromise ourselves. If you want a good relationship between two people, there should be no such contradiction and it should be resolved as soon as possible. If my brother really needs money, he can think of other ways, and he doesn't have to lend his credit card. Therefore, getting the credit card back is also an option.
03. Break up with your boyfriend.
This is the most extreme way. After all, this is already before marriage, but it is also the best way? If the first two schemes can't be realized, then use this method directly. After all, you are all getting married. If you can't handle this matter well and you still need to have conflicts for a long time, then there is really no need to be together. Because there are bound to be more and more contradictions after marriage, it is better to stop loss in time now and not to continue. This is a good result for both sides.
In fact, treating this kind of thing is nothing more than three results: the man compromises, the woman compromises, and it ends in discord. If the first two don't work, break up. But this kind of thing is actually very easy to negotiate. After all, it will be a family. There is no need to make things so ugly. Tolerance is great. Everyone should be tolerant to have a happy family.