Cabrón is a strong, informal Spanish word that can mean 'asshole' or 'jerk', but it has many nuances depending on the context and region. While it can be offensive, it's also often used among friends in a playful way or to describe someone who is tough or cunning.
In this song, the singer admits, "Admito que a veces fui un cabrón" (I admit that sometimes I was an asshole). This shows a moment of self-awareness and regret, making the word particularly impactful as it reveals a flaw in the narrator's character within the relationship.
Carín León is not asking for forgiveness here. He is asking for a verdict. The title line is the whole request, repeated until it sounds like exhaustion rather than anger: "Vuelve o vete" (Come back or leave). He will take either answer. What he cannot take is the waiting, and he says so while admitting he earned some of it: "Admito que a veces fui un cabrón" (I admit that sometimes I was an *sshole). His one condition is about the accounting. Remember the behaviour if you must, but remember the rest too: "Y me recuerdes por mi forma de querer" (And you remember me for the way I loved).
The second verse drops the argument and starts listing, and everything on the list is small and physical: "Ya no sé qué extraño más" (I don't know what I miss more anymore), the light left on, "Si recibir tus 'buenas noches'" (If it's getting your goodnights), the mornings. Then comes the bargain, which is where the song turns bleakly funny. He wants his heart back, "Pero devuélveme el corazón" (But give me back my heart), and admits in the next breath that it does not work any more, "Aunque ese no funciona sin vos" (Although that one doesn't work without you). He says he will keep it anyway, as a souvenir of the two of them.