Liam and Noah (both boys)
For Liam, Noah means everything. He was so "trained" to do only what Noah commands that without him, he has no idea what to do. He knows of things that he would like to do, but he never does those. Even when Noah is not around He misses Noah and looks at people without even knowing what society expects him to do, he talks to nobody, think about Noah and plays alone with Nameless (the bear). Oh, and he can feed (they are vampires). But Noah was supportive that Liam should give in to violent urges. Of course, never towards Noah, but towards other people was always fun to watch.
PS: I'm a bit sick and very, very tired. So I don't know if what I wrote will make much sense XD