Hm, I know that feeling. But if you look closely, Mafuyu sure love Ue for who he is. Like after their 2nd perform, Mafuyu jumps to him for hug, he even make music that for telling himself (and other) that's okay to let go, didn't he? Maybe he hasn't fully move on from Yuuki, after all everthing was 'first time' Mafuyu had, he shared it with Yuuki, so it must be hard to let it go just like a plastic bag. And I got a spoiler that after this chap, there's a storm will coming, hopefully in that upcoming storm, Mafuyu will be more 'active' with Ue like he used to be when he with Yuuki.
Why do I get a feeling that Mafuyu only like Uenoyama cause he sees Yuuki in him especially when he can’t sleep cause he saw a similar clock in Uenoyama’s room. I don’t wanna to be negative and all but I just can’t fully grasp in it. I hope Mafuyu likes Uenoyama because he sees something special in him and not related to Yuuki.