He didn't kiss her because he didn't think he deserved her or 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 more hurt when she lost him. Knowing that he loved her could also make her more willing to risk herself by continually giving him her blood, or she could just be more at risk by spending more time with him.
