Like Luke, Nick is a mystery, even though he exists in the narrator's present, instead of just in her memory. From the beginning, the narrator considers him to be a suspicious character:
He's too casual, he's not servile enough. It may be stupidity, but I don't think so. Smells fishy, they used to say; or, I smell a rat. (4.6)
While she is super-observant, and perhaps paranoid, it's true that Nick doesn't seem to fit into his position. But despite her suspicions about Nick, the narrator is immediately attracted to him. Even at the first Ceremony we witness, he keeps trying to secretly touch her foot. They kiss madly and illicitly in the dark. For most of the book, though, he serves as a symbol, a flag that goes up when the narrator is supposed to visit the Commander.
By the time the narrator and Nick start having sex near the end of the book, she is desperate for a companion and pours her heart out to him. She acknowledges the danger and potential stupidity of this:
[…] how have I come to trust him like this, which is foolhardy in itself? How can I assume I know him, or the least thing about him and what he really does? (40.17)
She seems to just trust her gut feeling and desire, even though all the previous events in the book would seem to advise against doing so. This is especially weird when we consider how she found him suspicious at the start. Now she says, "being [...] with him is safety" (40.17). Is it? She wants him to be the father of her new potential baby. Is he?
While the narrator tells Nick everything, he seems to tell her nothing in return:
He on the other hand talks little: no more hedging or jokes. He barely asks questions. He seems indifferent to most of what I have to say, alive only to the possibilities of my body, though he watches me while I'm speaking. He watches my face. (40.20)
The narrator seems to feel he loves her, but we have to take her word for it. She seems to give him too much, and when the men in the black van come to get her, she immediately wonders whether she should have believed in him after all. The last thing he tells her is to trust in him. Do you think he's trustworthy?