This is set in the OT+ AU, where the Guardians Oath doubles as a Marriage Oath.
The Guardians had a lot of different ways to say 'I love you'. Most of the time, those particular three words were never uttered.
They were too easy, to small to encompass everything that they had.
So they said it in other ways.
Sometimes it was the little things, the physical things – cuddling at night, touches that were gentler that usual, sitting together or playing together or a dozen little things that they did for each other that they wouldn't do for anyone else.
But the way they said 'I love you' that really confused other spirits, whenever they were caught, was the way they spoke to each other.
Oh, they used the pretty words, the praise and the passion, but those were for them alone, not to be shared with the rest of the world.
No, none of that was for other spirits to watch and comment on.
Besides, most of them were uncomfortable with it when out in public anyway.
To outsiders, the way they spoke to each other sounded like teasing at best, downright cruel at times.
Especially when they got onto holidays, or Jack and Bunny got into it, usually culminating in Bunny chasing a laughing Jack around while yelling threats.
More than once a spirit pulled one of them to the side, sometimes in 'concern' and sometimes out of genuine concern, but they wouldn't understand, didn't understand the few times any of them tried to explain.
Then again, unless they were a spirit specifically tied to something related to humor, most spirits couldn't recognize fun if it came up and licked them.
Jack would know.
...Don't ask.
But what those so concerned spirits never seemed to notice was the lack of bite behind the words they flung at each other, the teasing eyes or quick smiles that accompanied the sarcastic barbs or sharp words.
And they would never understand the emotions behind all the banter, or how some emotions are too deep to be put on public display.