I think this is because he is punishing himself for not being able to choose correctly before, even though he didn't know Utou's feelings, he feels he doesn't deserve Utou (and maybe that's why he was desperate to fulfill what Utou saw in him ) so he doesn't want something that makes him feel he has the chance to go with Utou. In addition, a person who is being manipulated hardly sees things properly, I just hope that this will break the mind control that Shiratori has in Sumi and he finally fight for what he wants and not for what society tells him he should want
That words from sumi hurts me too, but one thing is clear he just only stay with shiratori for being protected from other alphas and control his heat.... as Anónimamente-Anonimo says Sumi is punishing about the choice he made he never feel deserves Utou, and Utou just only can thought in Sumi Happiness even it is without him.
I just want Utou and Sumi do something they both always thought things but never talk what they really want... and finally do something like fight to find they're happiness... even i ship them so hard RN just want boht of them be happy i dont care anything more.
"The biggest reason is so that he doesn't ditch me"
I don't even feel sorry for him like he's ready to accept him not caring about utou anymore if he didn't find out about that fckrs plan he was willing to be with him happily.
Idk what happenes to both of them just let utou be happy.