Idk what you are reading but I have seen yuu being kind of dissapointed and sad when he tought Chiaki had a gf or when he tought Chiaki was a playboy and Chaki is always noticing Yuu's microexpressions like when he is worry and stress but doesn't say anything, like that scene where they need to go somewhere and Chiaki's friend his daughter offers to drive them off and Yuu's is worry because he doesn't feel confortable riding other people's car unless is chiaki's and he doesn't know how to decline the offer and while he is having all this thinking process in his head, Chiaki steps in and said that the 2 of them will use the truck, the Moments are there is just that is not straight to your face and this seems a slow burn and yuu's thinking process always tend to rationalize everything like when he was relieved that Chiaki didn't have a gf he thought it was because a sense of inferiority complex or if his heart was beating fast was because of lack of excersise
I don't want to jump to conclusions, but I thought there would be romantic feelings between them. Why is it taking a different turn?