Monótono translates to "monotonous" or "dull". It's a descriptive word that captures a feeling of sameness and lack of excitement, which is particularly poignant in the context of a relationship.
In the song, Paty Cantú sings, "Se ha vuelto monótono el amor" (Love has become monotonous). This line reveals a central theme of the song: the fading passion and routine that can creep into a long-term relationship, making it feel stagnant and unfulfilling. It's a relatable and emotionally charged word that makes you want to know more about the story.
Paty Cantú opens with the confession most songs save for the end: "Cuando mienten mis labios y te dicen te amo" ("When my lips lie and tell you I love you"). Nobody cheated and nobody walked out — the problem is that nothing happens anymore. "Se ha vuelto monótono el amor" ("Love has become monotonous"), she sings, "Se ha hecho otra costumbre sin razón" ("It's become another habit without reason"). The damage came from the years themselves: "Tanto tiempo llevo a tu lado, lo que fuimos me ha congelado" ("I've been by your side so long, what we were has frozen me").
The chorus names what is actually keeping the two of them in the room, and it is where the title comes from — "me da miedo aceptar que seguimos solo por estar" ("I'm afraid to accept that we continue just to be"), "y evitar así la soledad" ("and thus avoid loneliness"). By the last verse she has looked through both doors and neither leads anywhere: "Si tú te vas si yo me voy, la soledad" ("If you leave if I leave, loneliness"), but equally "Pero si estás y si yo estoy nada será" ("But if you are and if I am nothing will be"). The song never picks one. It just falls back into the wordless "Tu tu turu" hook it opened with.