Intereses literally translates to "interests," but in this context, it refers to financial interest or debt. It's a clever play on words, as "intereses" can also mean general interests or hobbies.
In the song, the phrase "pagarás con intereses" (you will pay with interest) implies that the person who took advantage of the singer will not only pay for their actions but will pay back with added consequences, like a debt that accrues interest. It's a strong, memorable word that adds a layer of depth to the lyrics.
This song is a classic tale of love and regret, but with a twist! Our singer is totally smitten, even though he knows this person isn't good for him. He admits, "no era tan normal antes de conocerte" [I wasn't so normal before I met you], suggesting this love has turned his world upside down. He wants to forget them, but they're stuck "enreda en mi mente" [tangled in my mind].
What makes it interesting is how he calls out the manipulation. He sings, "por más que me resisto con las mismas mentiras vuelves a convencerme" [no matter how much I resist, with the same lies you convince me again]. He feels taken advantage of, warning, "te aprovechas de mí... pagarás con intereses" [you take advantage of me... you will pay with interest]. It's like he's saying, 'You think you can keep playing games? Well, there's a price to pay for breaking my heart!'