91 Days...

Spoilers.... Here's your answers. Avilio found out just how empty his revenge was, especially after it cost him his friends life. He was expecting something after it was all over, but in the end he was just empty. He'd killed his best friend. There was no release from his pain. No reason to keep going. There was nothing left for him. So when they reach the ocean, Nero puts Avilio out of his misery, something Avilio wished he'd done all those years ago. (which was expressed in campfire scene). That's if you want to believe Nero killed him. But it never showed Avilio's death... He may have just fired the shot as a way a venting all his frustration at Avilio... metaphorically killing him... and then left Avilio there. Personally, I think he died.