Pisteando is a colloquial term in some Spanish-speaking regions, particularly Mexico, that means "partying" or "drinking alcohol." It's derived from "pista," which can refer to a dance floor or a track, implying a place where one goes to have fun and drink.
In the song, the lyrics "tu recuerdo está pisteando aquí conmigo" (your memory is partying/drinking here with me) use this slang to personify the memory of a lost love. It suggests that even in his sorrow and drinking, the memory of the person is a constant, almost active, companion, making the act of drinking a shared experience with the past.
Río Roma are a pop duo and Gerardo Ortiz sings regional Mexican, and the song puts both of them on the same barstool. It opens on the part nobody asks about after a breakup — the performance. "Desde que te fuiste todos preguntan por ti" ("Since you left, everyone asks about you"), and the answer is "finjo una sonrisa porque no sé qué decir" ("I fake a smile because I don't know what to say"). Then a small negotiation he loses: "Iba a pedir un trago, pero ya me arrepentí" ("I was going to order a drink, but I changed my mind") — and orders the bottle instead.
The chorus refuses the excuse the whole genre usually offers. "Todos me dicen que te olvide, pero no me dicen cómo" ("Everyone tells me to forget you, but nobody tells me how"), and then the line the title comes from: "Yo no tomo pa olvidarte, tomo pa extrañarte más" ("I don't drink to forget you, I drink to miss you more"). The bottle here is company rather than anaesthetic — "tu recuerdo está pisteando aquí conmigo" ("your memory is drinking right here with me"). Halfway through, the two singers break character to toast each other, "¡Salud, échele!" ("Cheers — pour it!"), and the round is for her: por ella tomo.