Gemela literally translates to "twin sister". It's a unique word to find in a song about heartbreak, which makes it very memorable.
Jessie Reyez sings, "Te hace falta encontrar una gemela que te quiebre el corazón" (You need to find a twin who will break your heart). She uses it metaphorically to wish that her ex meets someone exactly like her—a "twin"—who will give him a taste of his own medicine. This clever desire for karmic justice gives the word a powerful, biting meaning in the song.
Jessie Reyez is not holding back in this song. She's singing about a love that was so intense it made her ignore her mother's advice: "Este amor me dejó sorda" (This love left me deaf). Now, she's stuck with the memory of this person, who treated her badly but still wants excuses. She says she can't escape him—"Te apareces en mis canciones / Aunque no diga tu nombre" (You appear in my songs / Even if I don't say your name).
Instead of just being sad, she gets angry and wishes him the same pain. She sings that he needs to fall in love with someone who will completely break him, so that "así de pronto aprendes" (so you suddenly learn). The song ends with a dark and beautiful image of a love that has died, comparing it to a rose that's almost dead and a red that's almost black. And then she says, with a twist, "Ese es mi color favorito" (That is my favorite color). She's finding strength and even a kind of beauty in the darkness of the experience.