Dottore was never one to fully trust anyone, nor be vulnerable openly. Endurance was all he ever knew, and none have endured him till now.
You.
You had pursued him across Teyvat, not for vengeance but fascination. Old hatred cooled to curiosity then something more as you chased him. And the cherry on top was that even the Rtawahists of the Academia noticed that your star charts pointed to him.
Even after all he's done and what he will do. Even if he's considered a monster. You threw yourself at him. And he greedily obliged.
The wedding was in secret, because he was a private man, and he wanted the moment to be his and his alone.
"We endure for each other, surely, my love." He says with possessive finality as he slips the ring onto your finger, that damn smile of his sharp as ever. But he really meant it.
Something tells you escape or divorce is not an option....