Conchinha literally means "little shell" and is the adorable Portuguese term for "spooning" or cuddling in a spoon-like position.
It's a sweet and intimate word that evokes a sense of closeness and warmth. In the song, the singer reminisces about a past relationship, picturing "Nós dois embaixo do edredom de conchinha na sala" (The two of us under the duvet spooning in the living room), highlighting the tender moments he misses.
Gaab and Dilsinho split this breakup down the middle, and the hook says exactly where they land: "Eu não quero mais, não quero mais / Eu não volto atrás, não volto atrás" (I don't want it anymore, I don't want it anymore / I'm not going back, I'm not going back). She's the one waking up to what she threw away: "Só agora você percebeu / Que ninguém jamais te amou como eu" (You only just realized that nobody ever loved you like me). He's the one insisting the door is shut.
What actually stings is the domestic detail he can't quite shake. He remembers the two of them "embaixo do edredom de conchinha na sala" (under the duvet spooning in the living room), her clothes still tangled with his in the closet. That's the real subject of the song, not the breakup itself but the mess it left in the apartment. The "Ta ta tarara" chant that opens and closes the track is just a clap-along hook; everything in between is someone talking himself into meaning it.