Why Zero didn't actually Kiss Yuki?

He didn't Kiss her because he didn't think he deserved her hoặc was good enough for her. He was a vampire, and at that time he was still at risk of falling to Level E. If he kissed her, told her how he felt and they became a couple, she'd just be thêm hurt when she Mất tích him. Knowing that he loved her could also make her thêm willing to risk herself bởi continually giving him her blood, hoặc she could just be thêm at risk bởi spending thêm time with him.