Negociaré means "I will negotiate." It's an interesting word choice because it personifies sorrow (pena) as something one can bargain with, rather than simply endure.
In the song, the artist sings, "Negociaré con la pena / Para que no me pegue tanto" (I will negotiate with the sorrow / So it doesn't hit me so hard). This creative use of the word highlights a proactive approach to dealing with pain, making it a memorable and thought-provoking lyric.
Pepe Aguilar treats heartbreak like something you can strike a deal with. He opens by admitting he's clearing her out of his system — "Estoy vaciando mi vida" [I am emptying my life] — and by the chorus he has a proposal ready for his own grief: "Negociare con la pena, para que no me pegue tanto" [I will negotiate with the sorrow, so that it doesn't hit me so much]. The terms of that deal are specific — a new window built for one purpose, "de mandarla al olvido" [to send her to oblivion] — which is what makes the song feel less like a lament and more like a plan, set against the horns and strings of a ranchera arrangement built for exactly this kind of ache.