Comparing the two, I still feel that the matter of brothers getting married is more important. After all, this is a major event in his good brother's life. As his good brother, how can he be absent?
Although the first date with the girl you like is also relatively important, this first time can start at any time. If you can't make a date today, the two of you can go on a date at another time. And if you choose to go on a date with your brother that day, your mood will definitely be affected. Guilt is definitely there, and it may even cause you to lose your mind during the date, and appear in a trance, which will greatly affect the quality of the date between the two of you. It might even cause a misunderstanding to the girl, thinking that you don’t like her and don’t want to be with her. To put it bluntly, it’s not certain whether you can pursue this girl. There is no need to ignore your good brother for someone you are not sure about yet!
And it is the only time in a brother's life that a brother gets married. Think about it when your good friend invites you to go. What reasons do you use to refuse? You can't tell your brother that you're not going on a date with the girl you like, right? This really hurts people's hearts. Maybe it will also create a impression in your brother's mind that you are a person who values ??sex over friends, and the relationship will deteriorate in the future.
In this case, you should directly explain to the girl why you were unable to attend your date with her on time. I hope she can understand. If this girl is considerate and very sensible, she will understand you. Of course, if this girl also has a crush on you, then the boy can directly invite the girl to attend his brother's wedding with you. This would be perfect.