The narrator of Brideshead Revisited - the vacuum at the center of the storm

Much of the second (of 3) sections in Evelyn Waugh's 1945 novel, Brideshead Revisited, concerns the lead-up to the ill-fated marriage of Rex, an ambitious, blustering, social-climbing, MOP (tho Canada-born and raised) and Sebastian Flyte's (I still don't get why that's his surname) sister, Julia. All sorts of obstacles arise, few to the credit of Rex, who thinks he can buy or bluff his way through everything, and he pretty much can. No reader could possibly expect anything good to come from this marriage, but literary characters are bound to their fate - we can't intervene and save them. So we watch another member of the House of the Marchmains make a bad decision and begin to ruin her life. Meanwhile, brother Sebastian's drinking and pilferage has gone even further, as they track him down in a hovel in Fez, where he's living with a German man who shot off his own toe to get out of service w/ the Legion; the narrator, Charles, goes on a quick mission to Morocco to try to get S back before his mother's death - fails to do so - but in this mission we see the complete ruination of Sebastian's life and his homosexuality is now an open secret. What about the narrator? He's now pursuing a reasonably successful, or at least fulfilling, career as an artist (architectural painting), but to this point in his life - he'a in his mid-twenties, he seems to have no relationships w/ either men or women (setting aside his college-years relationship w/ Sebastian). He's not a "naive narrrator," in that the novel is told from the vantage of an older man looking back at his youth and his follies, but he's the vacuum at the center of the storm - we know surprisingly little about him other than his awkward relationship w/ his emotionally distant and at times emotionally cruel father; he's everybody's friend (although Lady Marchmain rips into him for his abetting Sebastian's drinking) but not close to anyone (a result of childhood - his father's distance, mother's early death?).