Q:

Why did Max leave the Citadel at the end of Mad Max Fury Road?

I guess Fury Road was a story of redemption, not only for Furiosa, but for every other character in search of hope and salvation, including Max himself.
That being said, why did he leave the "green place" at the end of the movie? The others were like family to him. They helped him redeem himself. He was a savage, animalistic man at the beginning of the movie, as he was "reduced to a single instinct: survive" (god I love that line!), and at the end, after all that bonding and trust, he finally becomes more human. He even utters his real name to Furiosa when at the beginning, he simply grunted.
My point is: Max has redeemedIn 1979’s Mad Max, Max, played by Mel Gibson, loses his wife and infant son to a vicious motorcycle gang headed by Toecutter (Hugh Keays-Byrne, who also plays the villain Immortan Joe in Fury Road). In a ruined world already tearing itself apart, this was the last thing tethering Max to the remnants of civilization, and severing that final tie set him adrift, which we subsequently saw in The Road Warrior and Beyond Thunderdome.
On one hand, he floats through this desolate existence, just surviving. But on the other, as we see in Fury Road, as well as the earlier films, the flame of who he once was still burns inside of him—he was a cop, a husband, a father, a good man—which is the part of him that