Ever felt that you like your (same gender) friend / BFF (even though you are/probably straight)

I have this friend, she's a girl, I'm a girl ; I feel like we really connect on a deep, emotional level. We tell each other secrets that we do not tell any other friends. I always can predict her thoughts depending on her behavior, mood and attitude. But for the past 2-3 months, I've been having these odd moods/feelings where I feel that I like her and sometimes I even imagine kissing her etc. but these moods come and ago, they could be there for 30 minutes but completely gone for the rest of the day and so on. I often think she's cute, but to be honest, she sometimes annoys me ; but I accept it. I feel like I have to protect her, when someone touches her I feel protective and it's as if I want to claim her and that she's MINE and MINE ONLY (?) I doubt that I'm bisexual, though, all my previous crushes/infatuations were all MALE. I've never felt this way towards a female friend, what does this mean?