I read TSH a little less than a month ago and I decided to start listening to the audiobook today. Amongst Tartt's great narration and unique voices for each character, I've come to realise that her impressions of Henry and Richard are not at all much different, and that's led me to a thought: could Henry just be an extension of Richard, an alter ego per se?
Everyone knows Richard admits to being a compulsive liar and we don't know the extent of the validity of his narration; therefore, how well can we believe the descriptions, or even the existence, of the characters? Far-fetched, I know, so let me take it back a notch.
By the end of the novel, it is clear Richard is obsessed with Henry, be it with the idea of him or all his attractive traits. Both have a love for Greek and aesthetics, both are compulsive yet skilled liars, and both have similar physical features; however, Henry has more money than Richard, comes from a higher social class, is more knowledgeable in Greek and literature, has more confidence, is personally closer with Julian, and has a romantic relationship with Camilla - these are all things that Richard wants or is ashamed of not having.
Throughout the book, Richard is ashamed to talk about his roots, lies to mask his lesser knowledge of ancient classics, and pines to know more about both Julian and Camilla. Thus, Henry and Richard only differ in luck and possessions, rather than personality and looks.
This leads me to my possibly far-fetched idea that Henry may be a fictitious character in the whole concoction that is Richard's narrative. In fact, Henry's character acts as a relief to everyone else's guilt after Bunny's death - he carries the blame as he is the one who comes up with the idea and physically pushes Bunny. Wouldn't Henry, then, be a good vessel to relieve Richard of his guilt, if he is to be the actual mastermind behind the murder?
Whatever is true, it is evident that Henry is just the idealised - Greek tragedy, may I say - version of Richard.