It's more on the line of their childhood love never got a closure. It never ended nor faded but got paused and things happened. When in love you don't get a closure, time gets stopped. You don't move forward because you can't understand why this happened and how this happened. Plus Yuki recently died, so it's natural for Mafuyu to still love him. Right now he is slowly moving to where Uenoyama is. So by the time he reaches him, Mafuyu would be happily in love with him. Right now, Mafuyu knows Uenoyama is his present and future and he is slowly looking forward while leaving his past behind but not forgetting it. Hope this helps.
one of the best replies i've read so far.
Does Mafuyu still love his childhood friend Yuki? That part is confused. Also, it is true that Yuki died for Mafuyu. If that is true then it is kind of sad.