It took me a moment to decide if I liked how you ended this. While slightly abrupt, it has a touch of mystery to it: did she decide from that image that she liked her looks? What were her conclusions? Did she ever fall into this melancholy again, and if she did, did a memory of this encounter cause her to pause, and perhaps smile... maybe not wistfully....
So many questions!
One note on the sex scene: In the paragraph "It was a sulky Argent," you have the statement:
Finally, Weiss withdrew his hands from his cock
I never 'saw' the movement which had him removing his hands from atop hers on the mirror to place them in a guiding position.
Overall, though, a very good one shot - short, sweet, nice PWP. Thank you for sharing!