Clara

This is a complex, beautiful song.

Based on the yearning, minor chords, and Chris Thile's keening vocals, I think the song is about a small, young family of husband, wife, and infant daughter, told from the perspective of the husband.

The daughter appears infant or very young because of the line, "Someday if she's hungry I'll bring her to you" -- she must be carried and fed by the wife; usually infants are breastfed.

Some lines are ominous, and my opinion is they refer to death and suicide: "Someday don't wake up" "It's gonna be a long night" "And the sun may never shine"

My hypothesis is that this song is about a young husband who is tormented by the belief that his wife doesn't love him ("Clara once upon a time your mother didn't love your father the best" and "Clara once upon a time your father knew he'd scare your mother away"). However, as he looks into her eyes "one-way mirror to my soul" he also realizes the truth, that he doesn't love himself, and scares himself.

"Singing lovers live in a dream that keeps coming true" - this line suggests to me that the husband of the song attempts to kill his wife and himself, likely with sleeping pills. Or maybe he just tries to kill himself. He says, "Go back to sleep" to both his daughter and wife, so perhaps he was alone in bed, had taken the pills, and wanted to be found.

In any case, the man writes the song for his daughter Clara, and makes references to how she will understand it when she is older "she's still a song to play/Someday but you're ready to hear it's for you".