Desaprovechao' is a colloquial, shortened form of "desaprovechado," meaning "wasted" or "squandered." It's a vivid word that captures a sense of regret and missed opportunity.
In the song, the artist sings, "Yo fui todo lo que quisiera tener, pero, desaprovechao'" (I was everything you'd want to have, but, wasted/squandered). He uses this word to express that his ex didn't appreciate or make the most of him, highlighting the pain of being undervalued in a relationship.
This song is a total mood! Gino Mella and Best are basically telling an ex, "Hey, I'm not just any ex, so don't treat me like one of many!" The singer feels completely taken for granted, saying, "Yo fui todo lo que quisiera tener, pero, desaprovechao'" (I was everything you'd want to have, but you wasted it). They were looking for something real in the relationship, but the ex was looking elsewhere.
It's a journey of getting over someone who really messed with their head. The singer admits, "Me siento mal / Pero por algo se empieza" (I feel bad / But you have to start somewhere). They're slowly moving on, "Bebiendo, fumando, en la disco perreando" (Drinking, smoking, dancing at the club). Even though they claim, "Yo no te quiero no te pienso ni te lloro" (I don't love you, I don't think about you, I don't cry for you), there's a clear sense of hurt. They even call out the ex for their lies and jealousy, remembering, "El único que soportó tus mentiras / Tus escenas de celos, el carácter, tu show" (The only one who put up with your lies / Your jealousy scenes, your temper, your show). But ultimately, they're focused on finding "paz mental por encima de todo" (mental peace above all else).