Platónico translates to "platonic" in English, referring to a type of love or relationship that is spiritual and non-sexual.
In the song, Sebastián Yatra sings, "Esa magia que tiene el amor platónico" (That magic that platonic love has). This word is interesting because it introduces a nuanced concept of love, suggesting a deep, idealized connection that transcends physical desire, which is a unique and thought-provoking idea in a romantic song.
Yatra opens by listing what frightens him, and the list is oddly specific. Tengo miedo de avanzar y de retroceder ("I'm afraid of moving forward and going back") leaves him nowhere to stand, and Tengo miedo de usar las palabras correctas contigo ("I'm afraid of using the right words with you") is the strange one: he is not worried about getting it wrong, he is worried about getting it right. Saying the true thing out loud would make it real.
Then the chorus does the arithmetic the title sets up. Fuimos segundos, falló el reloj ("We were second, the clock failed") and Por un segundo perdimos dos ("For a second we lost two") use segundo as a ranking and as a unit of time in the same breath, so the two of them are both late and runners-up. What keeps it from turning into a complaint is the line he settles on: No fue el primero, no por error ("It wasn't the first, not by mistake"). Coming second is the point here, not the consolation. He gives up the rest of it too, in En tu historia no pretendo ser el único ("In your story I don't aim to be the only one"), which is a lot to hand over in a love song, and he sounds like he means it.