La neta is popular Mexican slang for "the truth". It's an informal and authentic way to say "for real" or "honestly".
In this song, Ivan Cornejo sings, "Pero la neta te sigo extrañando" (But the truth is, I still miss you). Using this slang makes his confession of missing someone feel more raw and sincere, like he's sharing a secret straight from the heart. It's a perfect phrase to learn if you want to sound more like a native speaker!
Ivan Cornejo opens this track by comparing the sweet early days to a harsh reality: "Enamorados empezamos / Tristemente, mira cosas han cambiado" ("In love we started / Sadly, look, things have changed"). He remembers the physical sensation of falling for someone—"Mariposas tú me dabas con tus abrazos" ("Butterflies you gave me with your hugs")—only to realize he is the only one left holding onto those feelings. He drops all pretenses with the Mexican slang phrase la neta (the honest truth, or no cap) when he admits: "Pero la neta te sigo extrañando" ("But honestly I still miss you").
He fixates on late-night calls that used to mean everything: "Recuerdo de las noches que tú me llamabas / Bien tarde solo pa' decirme que me amabas" ("I remember the nights that you called me / Real late just to tell me that you loved me"). Even though he knows obsessing over the past hurts him—"Yo sé que es malo para mí" ("I know it is bad for me")—the hours drag without her. He gave everything to make her happy, and now he is stuck trying to wipe her from his mind while time crawls by.