Lástima translates to "pity" or "shame." It's a common word, but its usage in this song is particularly poignant and impactful.
The singer repeatedly uses "qué lástima" (what a pity/shame) to express regret and sorrow over a relationship ending, despite his resolve to leave. This repetition emphasizes the deep emotional conflict and makes the word resonate strongly within the context of the lyrics.
This song is a powerful goodbye, a moment of walking away from a relationship where the singer feels misunderstood and unappreciated. They believed this love would last forever, even calling it a "amor del fuero de toda la vida" [love of a lifetime], but now they realize it's not enough.
The singer is blunt, saying "no tuviste el valor de ver quién soy" [you didn't have the courage to see who I am]. They're not going to cry or say they don't deserve this, because they admit it's "probable que lo merezco pero no lo quiero" [probable that I deserve it but I don't want it]. It's a sad farewell, but one made with a sense of self-respect and the hope for something better, as they declare, "me despido de ti y me voy" [I say goodbye to you and I'm leaving].