Maybe he's embarrassed by it. I mean I assume this 'he' is your boyfriend or a potential guy you like so just think about it from his perspective "my brother's in jail" doesn't really attract the ladies.
I don't want to seem rude....But does it really matter?
I mean....It's HIS family.It's up to him if he wants to let people know.
If HE spent time In jail and never told you I guess that would be kinda strange.
But it's his brother......
My dad has like 11 brothers and sisters.
And I know very little about them.