I can see this jp comment happening but the reason they don't get back together is because shinobu returned fumi's feelings.
There seems to be a possibility that Sakura and Nakanishi weren't dating. "We had sex," "I'll make her happy," and "She's at my house now" are all just Nakanishi's perceptions at the time. It also seems like he's avoiding saying they were dating. Kyoka wasn't a party to the story, and it's unclear how much of the facts she confirmed about choosing Yuma being the right decision. In the scene at Nakanishi's house, it's unclear who the other person was, and the suggestive remarks lack conclusive evidence. It's hard to believe that Sakura, who was thinking of Shinobu right up until Nakanishi penetrated her, would suddenly fall in love with Nakanishi just because they had sex. Even now, Sakura and Nakanishi are either not dating, or if they have a relationship, it's at best just a casual sexual relationship.
8 minutes ago