It was one thing to make a mistake; it was another thing to keep making it. I knew what happened when you let yourself get close to someone, when you started to believe they loved you: you'd be disappointed. Depend on someone, and you might as well admit you're going to be crushed, because when you really needed them, they wouldn't be there. Either that, or you'd confide in them and you added to their problems. All you ever really had was yourself, and that sort of sucked if you were less than reliable.
Logical thinking keeps you from wasting time worrying, or hoping. It prevents disappointment. Imagination, on the other hand, only gets you hyped up over things that will never realistically happen.
Peter was, simply, what a person would look like if you boiled down the most raw emotions and filtered them of any social contract. If you hurt, cry. If you rage, strike out. If you hope, get ready for a disappointment.