Lyrics of Venn diagram

I have lost you to sleep again
Sleeping as we do on opposite sides of a venn diagram
I read the time in shadows on your wall
The shards of light through the slats on your window

I ease myself from under your languid arm
I fumble on my boots and hear you breathe through your alarm
And i disarm it for you, you rarely heed it anyway
I wouldn't want it to intrude upon your dream
School bell ring, messing up the play

A note, penned clumsily in this century's type-ruined hand
Saying "gone down the shops for a walk
I'll bring back some sandwiches"
And then i kiss your face, the black and the blue
I tie it into my laces, i don't want the wander blocking up the view

I stumble out into the afternoon
I'm still salty from drink and the late night pool
And i'll be gone an hour at most, you will be more diagonal
And i've a head on me in the post, i know, a castle swallowed in the swell