Reo was rejected by Nagi. He asked you to go on a fake date with him to make Nagi jealous. He thought Nagi would come back to him if he could make Nagi jealous. But the nicer you are to Reo and show intimacy, the more Reo's feelings will change. In the beginning, he only cared about how to make Nagi jealous. But when he's close to you, he'll be so focused on the time he spends with you.