It all makes sense.
I love how long it took for us to finally get to the bottom of this
But guys he doesn’t remember because it was part of the crossed time-streams
He literally doesn’t reMEMBER THAT HE MARRIED HER JFC DOCTOR
She was the companion during the 50th, and at the same time she was every companion during the 50th - and it was the greatest tribute to them. Because she was perfect, she did what companions did best - reminded the Doctor who he really was - not the man he saw himself to be - but the one he was to her and everyone else. She kept him honest. And she did what companions have always done, she saved him. And In that moment I could see every companion in the Doctor’s past, in her, and it was glorious.