I linked the mentioned picture a little higher in spoiler. In the NTR route, when Miru and Will are talking on the phone, Miru literally says: "I let him play with my tits for a bit". But you can see in the picture that it's not just tits, and that Miru is not completely honest. If this picture had been included in this dialogue, then everyone would have immediately known that Miru was lying. But Ocean doesn't want to immediately reveal Miru's cheating to the players, not even in the NTR route. When they talk, Miru is naked, and in my opinion, by this time she has already fucked the krayt guy, who is still in the apartment. Look at her eyes and body language in every picture, it gives it away. But maybe no one notices this, because everyone only reads Miru's body and the dialogue. This is mainly due to Ocean's visuals, since in almost every picture in the game the characters get a sharp and clear image, but the background is always blurry and not clear. This is what happens in these pictures, it's a bit dark, Miru's body is sharp and clear, but the background is usually blurry. However, if you give the picture a little brightness and sharpen the image a little, I think the answer is there. Miru is not alone in the apartment, and someone is sitting on the couch. And if this is true, then it's understandable why Miru says at the end of the scene: "I'm tired"...
And now don't judge me, because this is just my theory...