Sepulcro is a powerful and somewhat rare word for 'tomb' or 'sepulcher'. It's much more poetic and solemn than the more common word, tumba.
In this heartbreaking song about losing a loved one, the singer compares his own dark loneliness to the "soledad de tu sepulcro" (the solitude of your tomb). This creates a chilling and unforgettable image of his profound grief, making it a key word to understand the song's depth.
Natanael Cano's "Amor Eterno" is a heavy song about losing someone you love forever. The singer is dealing with a profound grief, telling us, "Tú eres la tristeza de mis ojos / Que lloran en silencio por tu amor" (You are the sadness in my eyes / That cry in silence for your love). He's so consumed by this loss that when he looks in the mirror, he sees the other person's face. The pain is so constant that he says he'd rather be asleep than awake, because it hurts so much that they're gone.
The chorus makes it clear this isn't just a breakup. He sings, "Como quisiera, ay / Que tú vivieras" (How I wish / that you were alive). He's talking to someone who has passed away. He feels a deep regret, thinking, "Sé que pude haber yo hecho más por ti" (I know I could have done more for you), even though he says his conscience is clear. The song ends on a note of hope in an afterlife, promising that "Tarde o temprano estaremos juntos / Para seguir amándonos" (Sooner or later we will be together / to continue loving each other).