I think he explained himself well enough in the press conference today and he's explained it again in the interview Sky Sports have just dropped. He knows it's time to go because physically and mentally he can't give what the job requires anymore.
He's 55, his back is fucked, his marriage is on the rocks, and if he stays in a high-pressure job much longer he'll give himself a heart attack. He's talking about wanting to leave football behind for a bit, to spend time with his dad and his children, maybe to patch up his relationship with his wife, to go on holiday, to rest and play golf, to actually be present in the lives of the people he loves. Being a football manager is a 24/7 job and it's slowly worn him down.
You can see it in him that he's become softer, more sentimental. In moments where people have criticised him this season you've seen people saying that the Pep of 2026 is miles away from the "We are tired? Fuck you!" Pep of 2018 and even the "academy is ready" Pep of 2023. The love and passion is still there but the steely-eyed intensity has faded and almost paranoid eccentricity has started to ebb.
The skinny feisty 45-year-old Catalan ideologue who took over in 2016 is now a slightly podgy 55-year-old honorary Mancunian who's without a mum, without a wife, and filled with (as he says in his last interview with Sky Sports) regrets. He needs to spend time on himself, on the parts of his life he's neglected in order to give as much as he can to the City job. I agree he's an addict, but I think he's an addict who knows he has to kick the habit now.