The pioneering sex researcher Alfred Kinsey broke from popular thinking on sexuality in the 1950s, theorizing that bisexuality was in fact far more common than previously thought. Fantasies can be a powerful vehicle to discovering new facets and depths of your sexuality - some people feel ashamed of dreams or fantasies that do not fit into their waking lives or partners, but even taboo-feeling fantasies may teach us something about who we are attracted to and why. Your dreams about your friend fall well within the range of normal sexuality. The curiosity your friend has sparked in you could be just that - same-gender wonderings - or it could be the impetus for discovering that you are bisexual, and may be attracted to other women in the future. But in actuality, most people fall somewhere on a spectrum of attraction, fantasy, desire, and action with people of all genders.
We are often called to label ourselves as purely sexually inclined one way or the other, either to be attracted to guys or to girls only, end of story.