Aferrado means to "cling to" something or to be "stubborn" about it. It describes the powerful feeling of holding on tightly to a person or idea, often against your better judgment.
In the song, the artist sings, "Sigo aferrado pensando que hay un nosotros" (I keep clinging to the idea that there's an 'us'). He uses this expressive word to capture his deep, emotional struggle of being unable to let go of a past relationship.
This song is all about a super messy, on-again, off-again relationship. Tito Double P lays out the whole toxic cycle, starting with the line, "Ni pa' que nos decimos adiós / Si mañana seguro me llamas pa' volverlo a hacer" (Why even say goodbye / If tomorrow you'll surely call me to do it again). He knows it's a bad situation and even says, "me siento pendejo" (I feel like an idiot), but he can't seem to break free. The relationship swings from high to low, which he describes perfectly as "lunes de desprecio y viernes de placer" (Mondays of contempt and Fridays of pleasure).
He tries to move on, admitting to "Un tequila y un culo pagado pensando en usted" (A tequila and a paid ass thinking of you), but he's still obsessed with her. The situation gets worse when he checks her phone and confirms she's with someone else. Still, he holds onto hope, looking at their old private photos and "aferrado pensando que hay un nosotros" (clinging to the thought that there's an 'us'). The title phrase, "perdido entre pase y pase" (lost between pass and pass), suggests he's caught in a self-destructive loop, fueled by this chaotic connection and maybe something more.