There is no "need" to tell anyone. If for some reason you absolutely have to get this off your chest, tell your big bro when you get one– but I would wait until the brothers have accepted you to do it, because otherwise they'll kick you out just for being the way you are, which is not cool. By the same token, maybe you shouldn't be openly bisexual– no one needs to know this about you except you.
The problem most guys have with openly gay or bisexual brothers is that they fear for the image of their chapter– and rightly so, because image *is* important for interaction between GLOs. This doesn't mean that you can't be yourself, I'm just saying that you should think about the implications for everyone else first. I don't know any gay or bisexual fraternity men at my school, but there are supposedly a few. Talk with your big bro after you've been a pledge for a while, and see what kind of reaction you get. if your chapter has a strong brotherhood, you should be ok coming out of the closet *after* you are initiated, because then everyone will hopefully do the right thing and accept you. Otherwise you risk one of those nationally-publicized sexual orientation discrimination stories. You need to talk to your school's Greek advisor about this too so you can figure out the best way to let everyone know.
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andrew watters
Theta Chi – ucla