Advice in talking with my sister?

It sounds like you're old enough that you don't live in the house anymore, right? I think that makes it especially cool if you talk with her about it, because even though you're her bro you count as an adult now.

It sounds like you found it out accidentally. And you can just go to her with that part, saying look, I heard x y and z. And I just wanted to let you know I'm really proud of you for being honest with your friends about this. If you ever need to talk or if you ever need anything, I just want you to know I'm there for you, okay?

I mean hiding that you know isn't all that fair to her. Since you already know she may as well know she has an ally within the family.

Oh, and also reassure her that you will Not tell the 'rents. Coming out is a hard enough process without people outing you before you're ready. :)

I think it's cool that you're there for your sister, and I hope the convo goes well. Good luck! :)

I would say to start out casually and in a casual setting where you two might both already normally be. Approach it as a situation in which you need her help in figuring out how to handle that would also respect a person's privacy as well as acknowledge the basic obligatory common courtesy one owes dear family members.

Such as, for example... Sis, I've come across a situation that I need your help/advice/input on in figuring out how to handle. Some information has come into my knowledge, through general conversation - not gossip - and I'm not sure what to do with it, who knows, and if anyone else may be entitled to know.

Then, gently, let her know what it is you know. Make sure you express that you respect her choices and her privacy, but since you now have that information, you may now be burdened with being unable to have open, unedited conversation with friends and/or family and whether or not that makes you uncomfortable in doing.

Without knowing the nature of yours and your sisters' relationship, it's hard to predict the interactivity of a given conversation between the two of you. Hopefully the both of you will have a meaningful talk about this and that it will end positively for everyone.

Just let her know that you are always there for her and that if she ever needs anyone to talk to that you are always there for her. Keep an open mind an a open heart. She will come to you in time. I would let her come to you when she is ready to.

Either wait for her to tell you, or start talking about gay and bi people and eventually hint at the fact that you know that she is bi, and talk to her about it!

Let her know, in private, that you know and you're ok with her sexuality. Also, you might want to ask her if she's out to your parents yet. That way you don't accidentally out her.

Give her this analogy:

Some people are born left-handed. Most people are born right-handed. Only a jerk would discriminate against left-handed people.

just treat her like you did before,if you feel you must say something to her ,just be cool and tell her how you feel and let her take it from there

I would let her come out to you in her own time.

I would tell her that i know, and see if she wants to talk to you about it. i wouldnt tell the folks, that is up to her to do if she wants to.