They’re all simultaneously attracted to the idea of each other holding Yuka and the idea of themselves— mainly Orie— as Yuka being held by one another.
Yuka cherished all three of them, supposedly, and her love for each of them complicates their feelings for each other in the midst of her death.
An interesting premise on paper, obscured by its unwillingness to let Yuka be more than a memory and limiting the boys’ memories of her to her body.
Their sexual encounters with each other are all fueled by a desire to embrace Yuka again, Orie has this prolonged interest in how Yuka had been held by the other boys, Tatsumi has photos of each of them being intimate with her, Suguru fucks Orie in his jealous rage over his relationship with her, which is accompanied by images of Yuka appearing in Orie’s place.
It actively makes Yuka’s impact on their lives seem uncompelling. We know next to nothing about her or the kind of relationship she had with each of the boys beyond that it was sexual, so we have no reason to recognize these things as borne of a deep connection to her because that’s not something we’re actually shown.
A brief conflict faced by Orie is whether or not he was really in love with Yuka or if he just liked the sex, and you might expect for the story to recount some of Orie and Yuka’s more emotionally intimate experiences, but the realization of his feelings is instead marked by his need to cum inside of her.
She is the crux of this manga and yet she dies in the first 3 chapters and is nothing but a sex symbol in the memories of who are supposed to be the lovers she left behind.
Without exploring their relationships with Yuka beyond sexuality, their behavior following her death comes off as obsessive at best. It also suffers from not exploring the boys’ feelings for each other unrelated to Yuka.
tl;dr — grief induced homoflexibility
Thirsty for Love