You WERE. And is your brother best friend, not yours. If he gets pissed off with your brother for this, he's stupid, and certainly not a friend. If he gets pissed off at you for this, as i said, no big deal. What can he do?
You dont wanna cause any kind of grudge...it's not your fault the girl likes you and not him. The sooner he'll realize it, the sooner his grudge will be water under the bridge.
Yeah, that's way too long. After six months I would assume the guy couldn't possibly have interest in me. I would recommend no longer than three months, and for some women any longer than a month will be regarded as too long.
There's always exceptions and extenuating circumstances, though. The #1 rule of dating is to work hard at understanding the preferences of the specific person you're interested in.