omg I lied I have more thoughts. So at the arc where they met Yui, Yui tries to protect Sayo's happiness by trying to kill Yamadera. Yui worries that by trying to kill Mei, Sayo has to kill or be killed. He tries to make him realize the gravity of that while also trying to kill Yamadera so that Sayo doesn't have to save him anymore and quickly get over his death and go back to living a "normal and happy" life he had before where he hides his vampirism.
BUT Sayo counters him, asking him why must he make a difficult choice? why can't everyone achieve happiness? he tells Yui theres more than one path and there Yamadera tells him that it's all right, they'll find happiness together no matter the path ahead. That's the significance of Yamadera questioning himself whether Sayo's happiness really exists with him let's all die
omg I lied I have more thoughts. So at the arc where they met Yui, Yui tries to protect Sayo's happiness by trying to kill Yamadera. Yui worries that by trying to kill Mei, Sayo has to kill or be killed. He tries to make him realize the gravity of that while also trying to kill Yamadera so that Sayo doesn't have to save him anymore and quickly get over his death and go back to living a "normal and happy" life he had before where he hides his vampirism.
BUT Sayo counters him, asking him why must he make a difficult choice? why can't everyone achieve happiness? he tells Yui theres more than one path and there Yamadera tells him that it's all right, they'll find happiness together no matter the path ahead. That's the significance of Yamadera questioning himself whether Sayo's happiness really exists with him let's all die