The songs of Homegrown
will always be defined by the story of Neil Young's relationship with actress Carrie Snodgress (who birthed his first son). The whole album was kept from the public for nearly 50 years because Young felt the material was too raw and personal. When Young found out Snodgress was sleeping around, it hurt him badly (though years later he confessed to having slept around on her, as well). This narrative fits in nicely with "White Line."
In "White Line," Young's talking about leaving a failed relationship and heading towards his true love.And I'm rollin' down
The open road
Where my true love, she lies waiting
Right now I'm thinking 'bout
These things I know
But the daylight will soon be breaking
Knowing the story behind the album, it's easy to fit Snodgress in as the failed love he's fleeing from. You were my raft
And I let you slide
So what's the true love he's running to? It seems like it's his music. When he sings, "That old white line is a friend of mine," he's referring to the white line that runs alongside roads (not cocaine, like the white lines in the Grandmaster Flash song
.) He's talking about the road itself - touring. But the white line of the open road is only his friend and the thing that takes him to his true love, not his true love itself. So, it makes sense that he's talking about touring taking him back to his music.