"Q.E.P.D." stands for Que en paz descanse, the Spanish version of "R.I.P." [rest in peace], and Gloria Trevi uses it to hold a full funeral for a relationship. The ex isn't dead, but as far as she's concerned he might as well be: "Ya te enterré" [I already buried you] and "Ya ni de lejos te quiero ver" [I don't even want to see you from far away].
The joke runs all the way through. She wants a mariachi playing while she sings loudly, tells him to keep his bouquets because "No reviven muertos ni sanan dolores" [they don't bring back the dead or heal pain], and says "Vete al más allá y olvídame" [go to the afterlife and forget me]. El más allá is the common phrase for the afterlife. There's a cheeky line about consoling herself with an Irish coffee, un irlandés. Then the ending: not in this life or the next will she go back to him. "Bye, bye. Mua."
Useful phrases here: ya fue is very casual Latin American Spanish for "it's over, it's done", tirar tierra (literally "to throw dirt") means to badmouth someone, and te pasaste means "you went too far". Se me cuida is a playful sign-off, like "take care of yourself for me".