"El Solitario" (The Loner) is a heartbroken guy's plan for getting through the nights after she stops loving him. He starts by listing what he did right: "Te llevé serenatas" (I brought you serenades) and he cut the best flowers for her. Then comes the hard part: "ya tú no me puedes querer" (you can't love me anymore).
The chorus is the best bit, and it is honestly a little funny in how specific it is. At night people will see him "hablando con las estrellas" (talking to the stars), a guitar in one hand and a bottle in the other, drinking and singing "hasta llorar" (until I cry) or until his strength runs out. If he falls asleep, he'll just wake up and keep going "hasta que amanezca" (until dawn). That is a full night shift of heartbreak.
Listen for the spoken bits too. "Alzate papá" is the singer shouting out his own name, and "Sírvame una copa" (pour me a drink) uses the polite usted form, the way you would order from a bartender. Useful phrase, maybe don't use it as often as he does.