Anything that is "weird," "strange" or "unlikely" in a dream is often a symbol... which is to say, not literal. "Sex" is often a symbol in a dream. Here's a link to its definition on this site...
sex
Please take special note of the second paragraph.
As to the question of your "real" sexual orientation, that's an answer only you can know and answer. The journey from the subconscious to the conscious can be tricky one, especially if you don't respect its language. In short, if something doesn't feel "natural," logical, obvious and/or in your best interest in your waking life, it's probably not right for you. Dreams require us to take a "leap"... a leap from the literal to the symbolic. Dreams should confirm what you really already know.
Hope that helps!