Eclipses refers to the astronomical event where one celestial body obscures another. It's a visually striking and somewhat rare word in everyday conversation, making it memorable.
In the song, KAROL G uses the word metaphorically to question why, if the moon and sun are meant to be separated, they sometimes have eclipses. She draws a parallel to her own painful love, wondering why she still remembers her ex without hate despite the hurt, much like the moon and sun briefly reunite during an eclipse.
In this song, KAROL G is up late, feeling the sting of a breakup. She's spending another night alone, filling her glass with tequila and toasting to a love that "me dejó en pedazos" (left me in pieces). She's trying to move on, but it's hard. She's even "blindando el corazón" (shielding her heart) from any more fake 'I love yous'. It's a lonely feeling, and she looks up at the moon for answers, asking why love has to hurt so much when it's not supposed to.
This is where the song gets really clever. She starts talking to the moon as if it's a friend who also has relationship problems... with the sun! She asks the moon, "¿Será que amarlo a él también te dolió?" (Could it be that loving him hurt you too?). She uses the moon and sun, who are always apart, as a metaphor for her own separation. But then she asks the big question: if the moon and sun are meant to be separate, "¿Por qué a veces hay eclipses?" (Why are there sometimes eclipses?). It's a beautiful way to ask why people who have broken up sometimes find their way back to each other, even for a moment. She's looking for hope, but also deciding she can't accept the pain anymore.