What does it mean for a boyfriend to book a hotel for his brother?

In the first case, the boyfriend may be lying to you, helping his brother book a hotel, or he may book a hotel himself and then do something bad behind your back. The second situation is that the boyfriend really booked it for his brother, and they have a good relationship and help him as much as they can. It's normal to think that they are all brothers.

In a word, if you have doubts or don't believe in yourself, you can either communicate with your boyfriend face to face and let him get rid of his thoughts. He knows what you think. If you really help your brother, he will tell you generously. If it is like the first case, you can also choose to collect evidence yourself and confront it face to face.