More than friends

well, i have this friend (of the same sex) and we are tighter than anyone else we know...but lately she's been flirting with me, she may be kidding around but now im starting to get feelings for her that i'm not supposed to! we almost kissed once... but we didnt because we where caught. i dream of doing things to her that are mostly sexual, I THINK IM A LESBIAN! is it normal to have these feelings for your best friend?