Pisteándome comes from the Mexican slang verb pistear, which means 'to drink alcohol'. It's a casual and very common term in Mexico, especially in Regional Mexican music like this song.
In the lyrics, the singer says, "Llevo varias noches pisteándome el dolor", which translates to "I've spent several nights drinking away the pain." This one word powerfully captures a sense of heartbreak and the attempt to numb emotional pain, making it a memorable and culturally rich term to learn.
This song is one big, desperate plea for a second chance. The singer has clearly messed up, admitting, "Que la regué, me equivoqué" (I messed up, I made a mistake), and now he's paying the price. He's spending his nights drinking away the pain and begging God to bring his love back. He can't even get through to her, pleading, "Bebé ya desbloquea mis llamadas" (Baby, unblock my calls).
He's completely miserable without her. He complains he's had "varias noches sin dormir" (several sleepless nights) because his bed still smells like her. It's a simple, direct song about heartbreak and regret, boiling down to one simple request repeated over and over: "Di que sí" (Say yes). He just wants her to say yes and take him back.