Fumiko and Ryuki spent all day and night together. Mostly the time, they had sex, blowjob, and handjob; he also licked every inch of her skin, and they had a great time together.
Of course, they didn't spend an entire day just having sex; they also spent time in the bath, eating, and in the evening, they went out to a restaurant and had a fun time outside, walking, talking, and holding each other hands.
It was a romantic day.
This was how Ryuki lost his virginity, and he was happy about it the way he lost it.
The next day was Monday, which meant he had to go to school, and Saki was also back at the house, so for a while, Ryuki was not going to have any sex with his mother. Of course, he could ask Rena anytime, and Rena would call Saki at her place, giving Ryuki all time to fuck his mother, but he wouldn't going to do that too often.
Moreover, even if he couldn't fuck his mother, it doesn't mean he couldn't have sex.