This Is How You Lose the Time War

I might leave a more "proper" review after a reread or two, but suffice it to say that I've rarely been so drawn in by a love story as by this novella, nor have I ever read a science fiction story that so adamantly ignores the details of an epoch-spanning time travel war in favor of using it as a vehicle for some of the most swoon-worthy epistolary passages I have ever read in fiction. This is a modern masterpiece.