The guy is contemplating or has already made up what he going to do. Suicide:
"There's been a hoot-owl howling by my window now for six nights in a row." The hoot-owl is an omen that something is going to happen, usually bad. Suicide.
"She's coming for me, I know. And on Wildfire we're both gonna go. We'll be riding Wildfire." She is already dead so the only way to make that happen is his death. Suicide.
"Gonna leave sodbustin' behind. Get these hard times right on out of our minds. Riding Wildfire." Whose minds? Our minds could be the multiple thoughts (voices) running through his head that he wants to be rid of. Suicide.