From the album The Lo-Fis
This is a love song that accidentally explains why its subject might feel isolated. Lacy thinks he's offering comfort by listing her exceptional qualities, but every compliment reinforces distance. She's mythical, unreal, a hundred out of ten. The sweater is practical. The praise makes her an exhibit.
Don't ya know? You're beautiful / You're different, unusual
The question assumes she doesn't know, which means he's revealing something or correcting her. But then 'I know you know' contradicts this. He can't decide if she's unaware of her worth or performing unawareness, so he hedges both ways.
I believe that you're a hundred out of ten
This is the exact kind of hyperbolic pedestal-building that makes someone feel more like a wonder than a person. He thinks he's countering her self-doubt, but grading her above the scale just widens the gap between how he sees her and how she might see herself.
You've been going through some things (I want you to feel better) / And if you're feeling cold (Here, put on my sweater)
The shift from abstract struggle to concrete gesture is sweet, but notice what he doesn't do. He never asks what the 'things' are. The sweater works for coldness. Her pain stays decoratively vague, something to soothe but not understand.
Seem so unreal, like you're mythical
He wants her to feel better while telling her she seems mythical and unreal. That's the contradiction he doesn't hear. You can't close distance by insisting someone is otherworldly. The praise itself is what makes her untouchable.
The song thinks it's building her up, but it might be doing the opposite. If everyone tells you you're too special to be real, eventually that becomes its own kind of isolation. The sweater is the only thing in the song that treats her like a regular person who gets cold.