Fingir means "to pretend" or "to fake," but it carries a stronger sense of performance than the plain English verb, implying someone deliberately acting a role to hide their real feelings. It is often tied to emotional masks people wear in front of others.
In this song, the verb points to the narrator admitting that putting on a front, acting happy or unbothered, has become exhausting, and that the pretending can no longer hide what is really going on underneath.
Most love songs pile on compliments. This one spends its runtime taking things away. It opens on "Bonita así, sin maquillaje caro" (Beautiful just like that, without expensive makeup) and keeps subtracting from there: no magazine spread, no chasing whatever is in fashion. "Bonita así, que no se vende por likes" (Beautiful just like that, not selling herself for likes) is the bluntest of them, and it dates the song precisely without turning into a lecture.
The better half comes later, when he stops describing how she looks and starts describing what she does. "Prefiere paz antes que rosas" (She would rather have peace than roses) carries more than any of the compliments, and "No promete, pero cumple" (She does not promise, but she delivers) reads like something you only write about someone you have watched over time. The closing argument arrives as a shrug: "Y si no lo creen, que lo pierdan ellos" (And if they do not believe it, that is their loss). Misael Soul sets all of it to 1960s soul, which is a strange backdrop for a song about not needing decoration, and exactly the right one.