While I've never been in a scenario quite like yours, I have felt the urge to divulge to someone.
I'm still figuring out my gender identity and everything, but as I was beginning this process a month or so ago, I kept feeling like I was bottling myself up, keeping all this stuff to myself, and it was consuming my thoughts.
Then I decided to ask the advice of a friend of mine who is a member of the LGBTQ+ (or whatever abbreviation you prefer) community, and while even that was a bit nerve-wracking, it did take a bit of the load off my mind.
It also helped when I found this site, where I could explore and learn about myself without any fear of retribution.

I'm not saying you should or shouldn't come out to your brother, but just sharing my experience.

I would suggest that you do what is best for your sanity. Maybe you can find something that you can do instead to alleviate your urge to tell your brother?
Best of luck!