>>49442339Rather than another invisible value that'll be a pain to increase, I'd tie it to something more concrete. After you've been the league with a pokemon, you can take them to a special dungeon that only lets you take in one pokemon at a time where you battle a bunch of other couples, and at the end you get a scene where you propose to them, but with enough ambiguity that gamefreak could say it's something else.
After that, they become your following pokemon all the time, even when they aren't in your party, they walk beside you, NPCs comment on it, kissing minigame, they get a ribbon, all that fun cute stuff. You really don't have to attach anything mechanical to it, it'd ruin the mechanic if you had to marry a bunch of pokemon to play competitive.
I'd also add some way to make your partner pokemon lay an egg without the day care.
