Probably because he didn't want to put the blame on the cheating dying bitch. So, he put it on the guy who last cheated with her, since he accepted Tatsumi as her partner but not Orie.
I think the biggest problem is that we never see anything about Yuka that justifies three guys destroying each other over her. She's not particularly beautiful. She's not particularly interesting. She's clearly utterly selfish and uncaring of the damage she causes. So, the big weakness here is we never see her being so great that it justifies them adoring her to this degree. She's just a crappy dying chick only wanting to screw as much as she can before she dies. And the damage she leaves behind..she doesn't care.
Except the third boyfriend didn't know he was cheating. The second boyfriend DID.
wtf? I still don't understand why senpai put all the blame on Orie? He was the one out of the loop till her "disappearance". It wasn't very enjoyable seeing how many things were not explained. Honestly, it became annoying. Their infatuation with Yuka honestly made it weird. There was no depth about why they really love her except that sex was great and they love her. I mean it was nice that they moved on at the end but the whole premise was lacking a lot.