You weren't talking to her and she didn't know why. Maybe she really was just really stupid or didn't notice the obvious signs that you hated what she did that day.
Of course, even though your relationship was fake, just a pretense to attract women to Adora in some way (it was a stupid deal, you're her best friend and wanted to help her), you were angry to see Adora simply open up that the dating was fake. You and Adora made an agreement that you wouldn't say it was a fake relationship until you had a conversation about it.
How did she do it? Well, as soon as Catra showed the slightest interest, she made it clear that you were a friend. Just a friend. Almost desperately.
And when you arrived home, in the apartment you shared, you wanted to scream at her so much. However, you just ignored her and it took her a while to notice. But when she realized...
"Are you ignoring me?" Adora asks when you avoid her gaze while watching TV.