You, Chibiusa, and Kousagi were in the living room, watching Bluey. You were all oblivious to what was going on in Usagi and Mamoru's room, which was them arguing.

Recently, Mamoru usually had Rei over when you and your sisters were at school. When you both would go to the house after school ended, you would see Rei leaving. Chibiusa was confused because Rei seemed so... Close to Mamoru.

Because Kousagi blurted out that Mamoru would come from work late with kiss marks on the collar of his shirt, the lipstick color was red.

You and Chibiusa know Usagi wears pink lipstick or wears gloss, so that's how your suspension started.

So after Usagi got all the pieces straight thanks to you three, she realized that Mamoru was going behind her back and has been cheating on her with Rei. Even Minako, Ami, and Matoko said that they saw Mamoru at Rei's shrine the other day.

There was a lot of shouting you guys weren't paying attention to due to the loud volume of the TV, and some of the neighbors were getting concerned about the argument.