He falls in love with her, because of her beauty, goodness, and child-like qualities. This bothers Grendel, because she has had to give up the life she would have wanted, being forced to marry the king, all because of him. She married the king in a ploy to save the kingdom from evil, himself. Just her very essence promotes goodness in other people where as Grendel the spawn of evil, feels himself being influenced by her, but since he knows he is evil, he fights back the feeling. Grendel chooses not to kill because doing so would have condemned him to being solely evil, which is exactly what he is trying to fight against.
2. He says that what man deems as evil, may not be the true evil but the actual evil. This sparks Grendel's interest, because this is the first time someone has said that maybe he's not the true evil, but in fact man is. This is what Grendel has been wondering all along.
3. "Things fade" means that every generation will have a new evil, and will need a new good to defend them against the evil. It will be a never ending cycle in time; as one evil is destroyed, a new one will take its place, but as the old evil faded so will have the good. "Alternatives exclude" means that if you choose to have a narrow opinion about evil, you will only follow someone else's opinion, instead of deciding for yourself.
4. The Shaper had provided his opinion for society to adapt as their own and now people would have to make their own decisions about things, including what is decidedly good and evil.
5. No, I don't think that murder is a necessary part of our world; it is a fatal part of human nature. If we considered this philosophy to be at all true, than everyone would go out and murder, if not only to defend themselves, but to further their existence. Grendel would just think that if he wasn't there to murder that then, his sole purpose is to murder.
6. He knew that a change was coming that would mean the end for him.