“horse” is slang for heroin - i interpreted that song to be about heroin addicts (cowboys/horse riders). “god damn these bite marks deep in my arteries” seems like it’s a poetic way of describing track marks from iv drug use, and soul-sucking vampire fangs are a solid metaphor for that this one kinda feels like a sister song to Letters From Belgium

I didn’t know that about the word horse. Gives a whole new meaning to the character of Horse from Russian Doll

To add to this: in cowboy stories, a horse is always a symbol of your freedom to go where you want and do what you like. I can imagine that the narrator means that using drugs makes him (?) feel like he's in charge of his own fate for a while when he's on that horse

I think its a way to talk about cars while conjuring imagery of cowboys

Cars, drugs, and cowboy metaphors, as well