Porquería literally translates to "filth" or "junk", derived from puerco (pig). It's a powerful, colloquial word used here as a very strong insult.
In the song, Nicky Jam sings, "Dile al noviecito tuyo... que él es una porquería" (Tell that little boyfriend of yours... that he's a piece of trash). This blunt and emotional insult reveals his raw contempt for his rival, adding a dramatic edge that makes you want to hear the whole story.
Puerto Rican reggaeton star Nicky Jam puts an ultimatum on the table in "El Amante" (The Lover). He is totally done hiding in the shadows: "Ya yo me cansé, no quiero ser tu amante" ("I got tired already, I don't want to be your lover"). The woman he is seeing stays in a relationship with a partner who ignores her, treats her badly, and never compliments her when she dresses up ("Si te vistes bonita, él no te dice nada" [If you dress up pretty, he doesn't say anything to you]). Meanwhile, Nicky reminds her that he loves how she looks even without makeup ("hasta sin maquillar") and brings the heat when her boyfriend leaves her feeling cold.
He writes this track directly as a taunt to the other guy ("Esta la hice pa' él" [I made this one for him]). He bluntly tells her to dump him by calling the partner out directly with "Dile al noviecito tuyo / Que él es una porquería" ("Tell that little boyfriend of yours / That he is garbage"). Notice the dismissive diminutive "noviecito" (little boyfriend), used here to shrink the rival's status and mock his hold on her. Nicky lays out the choice clearly: she can keep suffering in that dead-end relationship, or step into the light with someone who actually values her.