At first I was thinking that confession was completely random and didn't make any since why Kobayashi would like her cuz it seemed she was straight. Looking at it again maybe those calls were from her father telling her to get back home and they just assumed she was a slut. She was hanging around the guy cuz she knew Uchida had a crush on him, but she herself never had any interest in him and the 18 guys thing was probably a lie. In the end they probably didn't get together, and Uchida likely saw it has a chance to get with Nakano. Unless she had some kinda sexual awakening from that kiss, but that's not really realistic. Probably shouldn't try to chase after straight girls...