For some reason, I can relate to Yukino. When you don't have a good outlook of yourself and think of yourself less worthy. You would want to find someone who accepts you. But when you see that someone who is good to you, you then start to fear: "what if I taint this person?" What if I hurt this person even more than this?" "What if the person gets disillusioned when they see me for who I am?" Questions that haunt you, because you've been used to being criticised you, words that spark a sense of intimacy reminds you of that low regard for oneself.
What Yukino has is actually the fear of intimacy, fearing that she will get hurt, just as she fears hurting anyone more than she already does.
All that said, poor guy. He is quite a gentleman.
