Art

Here's a take:

This is the 1950s/60s (look at the fashion and style cues, interior decor color scheme), the 'affair' was a highschool relationship leading up to prom night, of which this is the culmination.

('Affair' did not used to be so strongly correllated with cheating on someone, it used to be used much more broadly, generally, neutrally, to just describe basically 'a thing that happened, that involved people'.)

Lady was/is head over heels in love with the dude... romantically, sexually, all kinds of attraction.

Guy loved her too... as a very close, best friend.

Turns out he's gay though, and has no sexual intetest in her.

And she genuienly did not realize that.

So, this is the woman buttoning up after having presented herself, and having been... something like rejected... and possibly she is very angry at Guy for rejecting her, possibly she is very angry at herself for not realizing it, possibly she has immediately gone into 'its ok, this is fine, we can handle this' mode...

While the guy feels like he has been lying to her this whole time, even though... he may never have directly, explicitly lied to her... and he is also now staring down the inevitability of this moment, as well as realizing that at least she now definitely knows he is gay, which means that his fate is very much tied to her.

You could also potentially justify this interpretation with where the character's faces and posture are in relation to both the viewer, and the lighting source of the scene.

Guy has his back to us, he's not open to us, the viewers, the public... but he is staring down the 'light of truth', his face is illuminated by it, though we cannot see it.

The Lady on the other hand, well, is facing us, is literally exposed... but her face is in shadow as she tries to lie to herself, or possibly now come up with some kind of lie to protect the Guy's now revealed truth.

The posture toward the viewer implies that we, the public, will be looking at her in the future to see if this secret is kept, we won't get an inkling from this otherwise in the closet man...

But the facial ighting implies that as he now lives in truth that he has shared with at least one other person, she must live in a lie, if ... his? their?... secret is to be kept.