Recaída translates to "relapse" in English. While it can refer to a medical relapse, in this song, it's used in a more colloquial and relatable sense.
It describes the moment of weakness when, after drinking, the singer knows she'll be tempted to contact an ex. It's a common experience for many, making the word both interesting and highly relevant to the song's theme of avoiding drunk dialing.
This song is a survival plan for a friend who is about to have a few drinks and a bad idea at the same time. Solange Almeida opens with a wish list for the night: "Espero que você tenha esquecido o carregador" (I hope you've forgotten your charger), "E que as amigas não tenham pra emprestar" (and that your friends don't have one to lend). No charger, no battery, no way to type a text.
The math gets specific and funny: "Tomara que só tenha 1% aí de bateria" (hopefully you only have 1% battery left), because "Se não é 100% de chance de procurar seu ex" (otherwise it's a 100% chance you'll look for your ex). She already knows how the night ends if the phone stays alive - "Eu sei que vai bater a recaída" (I know you'll relapse) and the next morning brings "a ressaca moral" (a moral hangover), which hits harder than the real one.
The chorus is the whole plan in five words: "Se beber não digite" (if you drink, don't text). "Bloqueia logo ele, finge que ele não existe" (block him right away, pretend he doesn't exist). It's not a sad song about missing someone - it's a friend standing between you and your phone, and the "para, para, para" that follows each chorus is basically her physically pulling it out of your hand.