We can do a quick summary 
They prepared the bed to go to sleep. She was already in bed. Suddenly, in the middle of the night, they decide to go out. They disappear for a considerable amount of time.
As soon as they return, without anything indicating that they went to a late-night store for anything missing, he goes to the bathroom to masturbate. So, he must have come back quite aroused? Did you notice that although usually everyone is in the bathroom, and they were there about two hours earlier when the guest showered, all four, this time she doesn’t enter the bathroom? She obviously knows what he is going to do.
As soon as he finishes, she goes into the bathroom and only washes her genitals. Immediately after she comes, they get into bed, she hugs him, they whisper extremely quietly, and she giggles a few times in between. Then they fall asleep.
They might have just gone for a walk, though 