I've had this fic stuck in my head and have no luck finding it so I come to the masters.
It's an older fic because Jim's family had not yet been dealt with in canon. During the course of the story his mom (and maybe a sister?) are mentioned.
Jim and Blair are in an established relationship. Jim is home making a romantic dinner for them when Caroline shows up unexpectedly. She's there to ask him to father a child for her; he turns her down. Blair shows up and is excited about an article he published. Jim deliberately outs them to Caroline.
Grateful for any help!
*Found by
moon_watcher99 ! No Questions in Forever by Myrna, link in comments