Pegaditos is the diminutive form of pegado, which means "stuck" or "glued". In songs and everyday speech, it's a very common and affectionate way to describe two people dancing extremely close together, as if they were stuck to each other.
In the song, KHEA uses this word to create an intimate scene, singing, "Te hice una canción para que bailemos pegaditos" (I made a song for you so we can dance very close). It's a fun, flirty word that perfectly captures the feeling of a slow, romantic dance.
This song is a whole conversation between two people in a super messy, on-again, off-again relationship. KHEA kicks it off by admitting he's losing his mind over this person. He says, "Me está matando la ansiedad" [The anxiety is killing me] because she's always in his head but never actually with him. It's that classic feeling of being totally obsessed with someone you know is probably bad for you.
Then María Becerra comes in with her side of the story. She's just as conflicted, singing, "Papi, yo te necesito" [Daddy, I need you], but immediately follows it up with, "¿Pero para qué quiero ir a buscarte? / Si tu love está por matarme" [But why would I want to look for you? / If your love is about to kill me]. They both know the relationship was never stable and is falling apart, but they can't seem to let go. They're stuck in a loop of needing each other and knowing they're better off apart.