Lyric discussion by TerminalHope 

Cover art for Broom People lyrics by Mountain Goats, The

I write down good reasons to freeze to death In my spiral-ring notebook But in the long tresses of your hair I am a babbling brook

This verse makes the song explicit for me. Seen in the greater context of The Sunset Tree as an album, we see that John's relationship with this girl was the only thing that kept him sane through his teen years. She is referenced in a number of songs, and you can easily see the shape of his relationship with her, but this verse is the most important.

You see, John has never disclosed to anyone about his abuse and been taken seriously. He's turned inward, away from his anger and sadness, and 'frozen' himself to keep it bottled up within. But when he meets Cathy he finds a kindred spirit and can finally talk about his feelings - he becomes a babbling brook when in the long tresses of her hair.

Here's where she appears in other songs...

"This Year" and then Cathy showed up and we hung out trading swigs from a bottle all bitter and clean locking eyes holding hands twin high maintenance machines

Cathy and John both had been abused or at least had a terrible home life, hence the "twin high maintenance machines"

"Dance Music" okay so i'm seventeen years old you're the last best thing i got going but then the special secret sickness starts to eat through you what am i supposed to do? no way of knowing so i follow you down your twisting alleyways find a few cul-de-sacs of my own there's only one place this road ever ends up and i don't wanna die alone

He follows Cathy though she is as damaged as he is, and finds out more about his own situation. But he knows the relationship is doomed (also, see Dinu Lipatti's Bones, which is entirely about their relationship)

"Lion's Teeth"

I am dreaming of you

He's thinking of Cathy. That's why this lyric only makes sense in the greater context of the album.

Also, one of the greatest albums of all time. Just sayin'.