If you don't mind my asking how do you determine if romance is to be added then? Do you make your characters with the assumption that they will eventually have a romance if your partner wants it? Do you write your characters without romance and only add it in if your partner seems interested?
In my experience romance is a lot like age. People will always default to their comfort zone unless forced to move beyond it by the plot.
I don't require ages for instance but I do tend to default to all my characters being 20-30. The only time I stray beyond that is if the plot requires a specific age outside of that range. So even if someone was to tell me, hey you can make your character whatever age it doesn't matter. I would still default to 20-30 because that's my comfort zone.
And in my experience romance is treated the exact same way. People tend to have a specific comfort zone in terms of either always writing romance into a story or keeping romance entirely out of the story. And absent any direct preference by their partner/interference of the plot they will just automatically add romance or remove it.
Usually determined by chemistry. Like, if the characters are proven to have the right chemistry and stuff then the story can be shifted in a more romantic direction.