We talked about predestination in "7C", about how everything, including past, present and future, is unalterable. It certainly seemed like a logical point, especially when the narrator found it impossible to kill Harlan because the latter was destined to die in bed with Eun-Ha.
The other avenue that we didn't explore, the one that we've been exploring all semester long, is, naturally, insanity. It's possible that the narrator is unreliable and batshit insane. His wife and doctor are initially adamant that the narrator's facial gash is an inflamed old scar, and at one point, he is suddenly able to see all the death wounds of those around him, and he appears to be the only one to see them.
His doctor thinks he is obsessive-compulsive - a sign that perhaps the narrator's been too absorbed into his work that he sees his work in his everyday life, and imagines that some catastrophic cosmic event is about to wipe out all life. But how could an astronomer, working with a bunch of other astronomers, miss such an event of impending doom in their observations? His work has consumed him, and his life revolves around his work such that he feels no emotion, no jealousy when he finds his wife in bed with his best friend. Harlan sees the madness in the narrator's eyes: "please/you need help/please/delusional".
Yep, he was plain nuts, just like most of the protagonists in all our stories. I suppose that's why he won that Poe award; Poe, too, was fixated with madness. It's just bizarre that a mild profession like astronomy could drive someone mad, and I'm no expert, but I do have a 99.6% grade in my Astronomy class right now, and it's the most serene class I've ever taken, especially when our professor dims the lights and plays a documentary of the night sky, and we all take a 5 minute nap. It just goes to show that you should never underestimate your nerdy best friend and sleep with his wife, just in case he goes nuts and finds you in his bed.