"As there is little foolish wand-waving here, many of you will hardly believe this is magic. I don't expect you will really understand the beauty of the softly simmering cauldron with its shimmering fumes, the delicate power of liquids that creep through human veins, bewitching the mind, ensnaring the senses.... I can teach you how to bottle fame, brew glory, even stopper death -- if you aren't as big a bunch of dunderheads as I usually have to teach."
~Professor Severus Snape
When we are introduced to Severus Snape, he is a harsh taskmaster, sure of himself, and with exacting standards that few could hope to meet. He is very intelligent and a master of his chosen field.
He doesn't seem to have much in the way of social skills and few, if any, intimate aquaintances. When we do receive information about his childhood, this sense of isolation and loneliness is increased. He was an outcast, as a child, taunted by bullies, possibly because of his sharp intellect and inability to relate to his peers. It is likely that he found solace in retreating to his studies. Further excelling in academics, he may have developed an arrogance that further isolated him, creating a vicious cycle of retreat into intellectual superiority.
He has a dark past, the details of which are not completely know at this time. We know that he now works for the side of the light, but do not know how or why that came to be. This mystery and his dark, brooding mystique leave many to view him as a tortured soul, seeking redemption.
He is often portrayed as a wounded spirit who has known little joy or love, or as one who has had these things cruelly ripped away from him. He is intense and controlled, but with strong passions that evident themselves in his temper and challenge us to get past his facade (for that is what we all believe it to be) and uncover the strong, passionate, fiercely loyal man underneath.
The question becomes, "How much of this is supported by canon, and how much is the fanon writer's tendancy to apply this archetype to Snape?" Despite the five books to date, we know very little about Snape as a whole character. We can see his appearrance, his evident attitude and other's reactions to him. We know that he was a death eater and that he now works for the good (possibly as a spy). We have had a few glimpses of his isolation and trauma as a teenager.
He is an adult character in a story that is essentially about children coming of age, and a supporting character to the star, Harry Potter. Everything else is supposition on our parts. The best we can do is to make sure that our theories fit the evidence given.
One of the ways to do this, is to develop a character profile. We can use archetypes - images and concepts based on mythical ideas and recurring themes of the collective unconscious. The infirmation that we have of him fits the idea of an inttelligent loner and brooding dark hero.
This is a concept that many find romantic and intriguing. We can believe him to be complex and sensitive with a mystery and tragedy that intrigues us. His harshness, pessimism and intriguing nature cause many to turn away from him, but are also obstacles to overcome to win his heart, loyalty and his devotion.
This tragic hero is a recurring character of dark romance. He is like the vampires angel or spike from Buffy: The Vampire Slayer. He has a dark past and and inability to let go and belong. He may be seeking a type of redemption, but not sure that he actually deserves it. The Beast from Beauty and the Beast hides in a dark castle, terrorizing all that come near, yet secretly longing for the young woman who will love him despite his appearrance. Sound familiar? However, due to the current ambiguity in canon, there is a lot of flexibility available for characterization.
One of the areas where this is extremely evident is in that of his sexual orientation and experience. Harry Potter is children's literature, and as such these concepts have not been and probably will never be addressed. I have seen well-written stories over the entire spectrum. Snape has been portrayed as a cloistered virgin, who due to his outcast status as a teenager and his later self-isolation, has never been in a physical relationship. Whether or not this is plausible, there is certainly evidence that whatever his sexual experience, his emotional experience may be lacking.
On the other side of the coin, you have a man who was part of a group that tortured and persecuted men and women alike, and may have participated in sadistic sexual encounters. He seems very controlled and self-aware. He could easily be portrayed as the dominant in a power exchange relationship, or as a submissive, seeking redemption and freedom at the hands of another. In writing this type of story, one would have to pay close attention to his emotional state and motivations.
We are bound only by our imagination and our skills to make our visions believable. That is probably one of the best things about writing Severus Snape. He is a witty, mercurial character, with a sharp tongue and shadowed history. We have a flexibility in writing him that is bound only by our interpretation of his history.