I understand from your question that you are wondering if you are bisexual or bi-curious, since you started developing feelings for a girl in your class, and also starting looking at other girls while you had crushes on guys in the past. I sadly can’t tell you if are one, the other or anything else, since only you and your life experience can give you an idea of that answer.
While exploring this side of your personnality might be an indicator for yourself and what you wish to discover, no one can truly tell you, but you. You might want to wait until you make any kind of coming out, or you might want to discuss your own feelings with some members of your family. Having someone to discuss with about all this questions and feelings should help you.
As for your roommate, starting by talking about homosexuality or bisexuality, opening a positive discussion on the theme might be a good start, trying to demystify and clarify what sexual orientations are, since you already know her opinion. If you think you don’t have enough information to have this discussion with her, a school or organization’s specialist like a sexologist or a social worker or a queer association could probably help you with it. Some of them could probably do a kiosk or a workshop to demystify sexual orientation in your school or campus.
I hope this helps you, truly,
Inge Rollin, Sexologue B.A.