It might not be so much about the sex/friend as about how you relate to yourself and how you need to learn to love yourself? Your friend could be a mirror you, especially if you don't have a sister to dream about. I believe we "are" every character in our dreams; they're our creations after all, our thinking them up. I wouldn't worry too much about your sexuality but I'd look at what you might be telling yourself about "you" and your relationship to yourself.