When Ash said he'd come back as soon as possible, Pidgeot didn't get his hopes up. It wasn't that he didn't trust his trainer, but he knew both their lives had changed and would change more as time went on.
Ash went to Hoenn and Sinnoh, stopping in Pallet Town at least twice in between but it was mostly business as usual. Training and battles, preparing for the next leg of his journey. In turn, Pidgeot would be so preoccupied with the younger Pidgeys and Pidgeottos that he didn't have time to languish waiting for the boy to come back for him.
That wasn't to say he didn't miss Ash, of course. Ash, Pikachu and the gang, Brock and Misty and all of their Pokemon...they'd been like his family. But these birds were a family to him now as well. Every day he would protect and care for his little brothers and sisters, and every day he'd wonder how Ash was doing.
Eventually, Pidgeot stopped wondering if Ash would come back. They'd grown older, they'd moved on with their lives.
And then one day, a teenage boy walked into the forest, his arm wrapped around the waist of a familiar-looking redhead.
"Pidgeot! Remember me?"
Pidgeot swooped down and landed at his side, and Ash smiled.
"I told you I'd be back. Sorry I took so long. You remember Misty, right?"
"Hey, Pidgeot," the girl said. Pidgeot crooned happily, suddenly all the time that had passed since their parting seemed like mere minutes.
Welcome home, Ash.