A little advice, please?

It's kind of simple, actually. Recently I just found out that I am bisexual for some unknown reasons, though it's kind of stronger towards men than women. Well, not kin of recently, since I've been keeping it for a few months already. Teh problem is that I don't know how long I could keep it down.

I would really like to tell anyone about this, since keeping something about you and acting like you're not it is very hard and frustrating. The bad news is that the society around me COMPLETELY rejects homosexuality.

Now I'm in stress; my sister have started to be aware that I could be a gay while my family is the last people I want to tell about this (because they are very radical about gays). My friends at college also see homosexuality as something wrong and disgusting, although their degree of dislike is milder than my family. My fear is that I may lose everyone if I tell the truth. But I couldn't keep it much longer; there will be more people like my younger sister who are sensitive enough to see me through.

So, what should I do? Just for fact, I am raised normally without experiencing sexual abuses and I used to like girls like a heterosexual guy would like.

Jam it back in, in the dark.