Maybe you would think someone you spent your entire life growing up with, shared DNA with, and who is from a more recent generation might be someone you could confide in and trust?

Maybe OP didn't tell his brother and his brother found out some other way- which, if he was so willing to put OP for such a petty reason, I wouldn't be surprised if that's the case. Also, what you're doing there? Victim blaming. Because you are either blaming someone for trusting their FAMILY or for being found out though no fault of their own. Outing someone without their consent- ESPECIALLY for the sake of causing them harm like in this post- is a shitty thing to do, and all the blame for it goes the same place it would with any other harmful act- on the perpetrator. Oh, and being "out" to even one family member is exponentially better for an LGBT+ individual's mental and emotional health, and can literally be the difference between life and death for some people, so expecting them to stay paranoid and closeted isn't exactly rational.

It doesn't sound like the collar was just laying around- if the brother and friend were dumb enough to cook up this idea, they're dumb enough to buy an electric collar specifically to be stupid with. There's also nothing that indicates that OP has any particular say in the use of the shock collar, if it is in fact usually used on an animal. My guess is that either they don't live there and only visit, or they do live there but only because they have no other housing alternatives and can't risk being kicked out. Which, if the second is the case, makes he brother even more of an asshole.