Amarrada literally means "tied down" or "bound". While it can refer to physically tying something, in this song, it's used metaphorically to describe a feeling of being restricted or trapped in a relationship.
The lyric "No quieres estar amarrada" (You don't want to be tied down) reveals the partner's desire for freedom and independence, making it a key word to understand the song's theme of a relationship ending due to a lack of commitment.
She calls to end it, and Jay Wheeler beats her to the punch. The song opens on that phone call ("Ayer recibí una llamada" [Yesterday I received a call]): she's tired, she doesn't want to be "amarrada" [tied down], and she's sure he's the one who lost. His answer is the title. "Yo tampoco te quiero, siéndote sincero" [I don't love you either, to be honest] is a pride move, and he admits it a line later with "Por el orgullo pensaré en mí primero" [Out of pride I'll think of myself first]. Notice the "tampoco" there: it means "either" or "neither", so the whole chorus only works as a reply to something she said first.
The best lines are the petty ones. "Bajando puntos llegaste a cero" [Losing points, you hit zero] treats her like a scoreboard, and "Pa' estar contigo, mejor con cualquiera" [Better off with anyone else than you] is just blunt. "Pa'" is the clipped, everyday Caribbean way of saying "para" [for, in order to], and "Bebecita" is a Reggaeton favourite meaning "little baby". By the end he's tripled down on himself with "Ahora soy yo primero, segundo y tercero" [Now it's me first, second and third], which is a bit much and clearly meant to be. The closing shout of "La Voz Favorita" [The Favourite Voice] is Jay Wheeler's own nickname, signing the track like a name tag.