Ok, so Noé and Vanitas exist in two different types of Vampire Novels. Explained below the cut, because it's long.
Starting with Vanitas: This man is in a tragic romance novel. He is the hero of the day, he is a charming and handsome doctor, he is the savior of all the beautiful people. He choose a strong handsome man to always be ready to rescue him and for him to always be ready to rescue. The entire time we see him he never asks anyone else to join him in his quest--just Noé, at the beginning of the story, immediately upon meeting him. And Noé lives up to his role. He is reluctant but starry eyed, strong and handsome and pure, 110% behind Vanitas's cause. We can see this intent in the way Vanitas, multiple times, flings himself into Noé's way. He makes sure Noé is watching when he kisses someone else (just to tease her, he says, fully aware that Jeanne as she is will never actually return those feelings.) He is listening at the door when his chosen lead has a "dalliance" with someone else. He immediately retaliates against this by allowing Jeanne to drink his blood, both discovering what exact experience Noé was having with Domi and furthering Noé's interest in him (I don't kiss and tell, with a hand over the wound.)
He has only a few purposes to his life at this point: Be a hero (save the vampires), fall in love and be loved (as stated by Luna and his own desire for salvation. What is salvation for a man who is unlovable? Those two scenes are placed where they are for a reason.), die. That's why he is acting all the time, that's why he says he'll do as he pleases, that's why when he saves someone it is theatrical and handsome and romantic. He's living out a romance novel in the time he has left and I truly think Noé is his leading man. He has allowed himself to be the leading man for someone else in Jeanne. He's willing to (and I suspect may actually be faced with the task) kill Jeanne, but he cannot and will not kill Noé. In fact, he plans on Noé being in his final act--the tragic part of his tragic romance. To die by the hands of the one he loves, to die knowing he is loved by the person who kills him. That he died himself, and with mercy. But this leads into Noé, who is NOT living in a tragic romance. Noé is living in a horror novel. He is afraid, and the people he cares about are hurting, and it has been placed on HIS shoulders to save as many people from the Horrible Terrifying Creature who Twists People before they can be twisted too far. We can see this in the fact that Teacher gives him instructions--these are not whimsical well wishes. There is not the kindness or love in Luna telling Vanitas he will find someone to love him, if he only opens himself to it. This is Teacher telling Noé on no uncertain terms: Do not give up your name--it is everything you are. Find the book of Vanitas and study those who interact with it, become enmeshed in their lives. Decide how this book is being used and what it means. For Noé, people he loves are already gone due to the monster that is Charlatan. And he tries to destroy it every time he sees her. And he even almost falls to it! (But Vanitas, in his romantic gestures, saves Noé before he can be taken, until he doesn't, because Ruthven obviously has a large hand in this corruption.) Noé is a consistent victim of this monster--first Louis, but also it is Amelia who we first see bite him without his permission, draining him of power that he NEEDS to save her, because his instinct (despite knowing, he has to know, he's seen it before) is to save her anyway. And he's got psychological trauma. He's got ptsd that results in bursts of anger and fear and causes him to act without thinking. His only weapon against this monster that could destroy him and his entire world is a man who doesn't seem to understand the extent to which Noé NEEDS him to succeed as often as possible. And so he's stuck trying to figure out his ONLY defense against this monster that twists people into shells. And then he finds out his teacher is also a monster. A different kind, but a monster nonetheless. And you have to wonder, seeing Misha, does he not wonder about his own upbringing? About the things his teacher has told him? Noé constantly has the rug pulled out from under him, is constantly getting blood taken from him without his permission, constantly having to drink blood because of his abilities without his permission, constantly being taken hostage. He's the protagonist of a horror novel who knows nothing about the monster except that it's terrifying and a threat to everything he cares about and he's been told by another monster that he's the special guy who has to figure out how to save everyone. And again, he's faced with someone he loves, someone he clearly is IN LOVE WITH, telling him that it's him who must kill them. Before they become a monster. Before they become someone other than themselves. His literal worst nightmare, coming around to repeat itself again. See, different genres. And it works best like this. If Noé was the one living in a romance novel, Vanitas wouldn't have lasted two seconds before he was swept off his feet. If Vanitas was living in a horror novel. Well. He already did. He'd collapse under the weight of another one.