Ik it's confusing, but I think what the Uke mostly meant is that he doesn't get hard with someone he likes, i.e. people who are good to him in general. Like he's fine with people he likes but he didn't like them sexually. He wasn't expecting to get hard with his nephew because A. He likes him as a person and 2. he's family. When he didn't get hard with the colleague, he was also aware that he was indifferent towards him romantically, so that probably started to break down that rule he had of not getting hard with someone he likes and vice versa. He actually got hard with someone he likes as a person for the first time with the nephew. He still doesn't want to accept his own feelings though.
Uke said he couldn't get hard if he's doing it with someone he likes.
Uke got hard while doing it with his nephew. So it means he really doesn't like him, at least in that way. He mentioned he agreed to do it, so the student could get it off his mind and focus on his upcoming exams.
But later on, uke said he couldn't get hard when he did it with his boss. So it means he liked the old creepy overconfident man?
Ugh. I don't like that guy. Esp, when he talked to Daisuke in the restaurant. Wish he's dead.