Cabrón is a versatile and strong Spanish slang word that can have many meanings depending on the context, ranging from 'badass' or 'awesome' to 'messed up' or 'a jerk'. It's a word that adds a lot of punch to a sentence.
In this song, Nicky Jam uses it in the phrase "No olvides que se siente cabrón" (Don't forget that it feels messed up/really bad). Here, it conveys a feeling of intense pain or difficulty, emphasizing how much he's suffering from the breakup. It's a raw and authentic expression of emotion that makes the lyrics very impactful.
Nicky Jam spends this whole song refreshing his phone. He opens on "Ya no sé ni qué hacer" (I no longer know what to do), watching the chat to see if she's online and waiting on one word: "bebé" (babe). The breakup wasn't even that dramatic, he admits: "No fue pa' tanto pa' acabar lo de nosotros" (It wasn't that big a deal to end what we had), which somehow makes missing her worse.
What he actually misses are small, specific things: the panties and a photo he kept, a rented Airbnb, a night out in Calella with four bottles between them. Now he's out at the club alone, "perreando en la disco triste" (grinding, sad, on the dance floor), and none of it fills the hole she left. "No entiendo qué me hiciste" (I don't understand what you did to me) isn't really a question. He knows exactly what happened. He just can't stop replaying it.