I hate that I can't hate you

So that was why she reacted that way. She must have gone over personally to dispose of the evidence. If Kuruga left behind a message for him, they would think he was involved in her death. But the reason they didn't must be because Aki found the message first and called Sumire over.

"I knew."

Yuhi didn't apologize. He knew there would be no use. Besides, he can't deny his responsibility in this. She must feel betrayed that he didn't tell her anything even though he has been careful this entire time with his words and actions. What he did by not telling her anything is the same thing Mamoru did. 

When he first entered a relationship with Sumire, he promised her that he would make her happy and treat her equally. But by hiding this from her, he has betrayed the promise he said that day.

"I hate you." She exclaimed. "I hate you so much." Her voice broke.