She sat two steps above him, close enough to see the curve of his shoulder, far enough to pretend she was just resting. The silence stretched, not uncomfortable but strange—the way silence feels when two people are both pretending not to notice the electricity between them.
The background romance should still have something to lose. Maybe it's forbidden. Maybe one character doesn't know the other exists. Maybe there's a time limit. Stakes create tension; tension creates investment. little teeny sex extra quality
She learned his name by accident: Arjun. She saw it on a building directory, then confirmed it through the whispered gossip of the mailroom clerk. He worked in “Special Collections”—whatever that meant. Some dusty archive of things no one remembered they had. The building had been a library once, a century ago, and somewhere in its depths there were still rooms full of brittle paper and forgotten ink. She sat two steps above him, close enough
To ensure readers don't get confused, give your "extra" couple a unique dynamic: Maybe it's forbidden
Perhaps that was the point. Not every connection needs to become a romance. Not every romance needs to become a relationship. Some things are beautiful precisely because they are small, because they ask for nothing, because they exist in the margins where real life cannot reach.
Side romances are often better for character development than primary ones because they allow for quieter, more authentic moments.