Spike could hear the disappointment in Wesley's voice, and he was sorely tempted to agree to give him whatever he wanted. Feeding from him wouldn't be a physical hardship, though it went against what Spike thought was right. Perhaps if Spike had cared less about him he would have been more willing, but Wesley was important enough to him that Spike wanted to treat him as well as he possibly could. He wanted Wesley to be happy, but he wasn't sure that he could stand making him happy by hurting him. If Wesley being unhappy was the other option, though...

"Why is it important to you?" he asked, his heart heavy.