I feel like....Uenoyama sees Yuki as someone incredible who loved Mafuyu, and Yuki sees Uenoyama as someone incredible who loves Mafuyu too, so I don't really think that it's heartbreaking for Uenoyama in a sense that's it's Mafuyu's ex, but that he is Mafuyu's ex and he pities him....
I feel like....Uenoyama sees Yuki as someone incredible who loved Mafuyu, and Yuki sees Uenoyama as someone incredible who loves Mafuyu too, so I don't really think that it's heartbreaking for Uenoyama in a sense that's it's Mafuyu's ex, but that he is Mafuyu's ex and he pities him....