In The Picture of Dorian Gray, why does Oscar Wilde depict homosexuality/overall sexuality in an ambigious way?
The treatment of homo-eroticism as a theme in The Picture of Dorian Gray is a part of the aesthetic backdrop that structures and also helps to color the novel. It is also used as a way to challenge the hypocritically-prudish surface of the Victorian society. However, there is much more artistic and historical value to the use of this theme, such as the motif of aestheticism.
A product of the Greek ancient cultures, Aestheticism aims to seek, explore, analyze, and honor beauty in all of its concrete and abstract forms. The Renaissance movement is a good example of this exploration of beauty. This period based its works on the revival of the ancient Greek ideals of aestheticism.
In the 19th century, Wilde's mentor Walter Pater revisited the ideals of Greek aestheticism in his studies on the Renaissance, advocating that a new aesthetic movement would prove that Art should not be used to educate, but to inspire--"L'Art pour L'Art": Art for Art's sake. This is the philosophical movement to which Oscar Wilde belongs.
The idea of homo-eroticism being a part of the Greek culture, and therefore part of the aesthetic mentality, is a product of Wilde's society of the mid 1800's. The writings of Aristophanes, Aristotle and Plato (who later recanted his thoughts) among others, brought out the rationale that male love was, in conclusion, a higher form of classical emotion. Regardless of his personal life, Wilde's inclusion of homo-erotica, or its undertones, would be indicative of his true aesthetic style. Colloquially he simply would have to add it "somewhere, regardless" because he is a true aesthete. This being said, notice how well the elements of aestheticism (and homo-eroticism) fit within the structure and theme of the novel.
First, the friendship between Dorian, Basil, and Lord Henry serves as the backbone of the plot: here we see the Greek aspect of homo-eroticism in that both men, Basil and Henry, admire a much younger Dorian for his physical beauty. Homo-eroticism works with this scenario because, thanks to it, both Basil and Henry unofficially "appoint" themselves as Dorian's mentors in life. This is a replica of the idea of "the love that dares not speak its name," as Wilde would say: the Greek dynamics between an older man and a younger man, where the older man serves as the "teacher" of the younger. Lord Henry would be Dorian's "teacher" in the indoctrination to his so-called "new Hedonism."
Homo-eroticism also helps to color the otherwise dark aspect of the novel's Gothic nature. This is because Lord Henry's admiration for Dorian brings out the best of his repartee of epigrams and axioms. This brings the atmosphere of the novel to a refreshing lighter side at some points. Had Lord Henry not been attracted to Dorian Gray, the novel would have lacked rich phrases such as:
The one charm of marriage is that it makes a life of deception absolutely necessary for both parties.
Hence, Wilde's use of homo-erotica would have been a required element to complete the features of an aesthetic work of art. This asserts Wilde's strong aesthetic persona and his credibility as a member of the movement. Although the topic raised eyebrows, Wilde would not use it alone to shock. That would be too simple. Instead he caused shock by treating the topic with as much art, class, and neutrality as any other topic in Victorian literature. It is not in what he says, but in what he does not say, that Wilde excels as an artist.