Sebek has said he has devoted his life to serving Malleus, and we get more insight into this during Halloween: Sebek explains that he reveres Malleus from the bottom of his heart, not only for his noble lineage but also for being a magnificent person he genuinely admires.
Sebek says that there have been times when he agonized over whether or not someone as unworthy as himself should be serving Malleus at all. He also confirms that he is not an official royal guard but merely in training, as he still lacks many requirements, but he intends to continue doing his best to become someone worthy of serving by Malleus’ side.
Sebek has said more than once that Malleus is the only reason that he is at NRC at all. When Lilia says he is “genuinely astounded” at how single-minded Sebek is about Malleus, Sebek takes it as a compliment.
It is possible that Sebek would have appeared at the school of his own accord even if he had not been admitted: he says that he has wanted to go to the school ever since Malleus enrolled, but he lacked the magic reserves and proficiency to fly there, and there is effectively no public transportation in Briar Valley.
Sebek says that while he had never seen the school before it occupied his every waking thought, and he memorized a book about it to the point that he could recite the content by rote.
Sebek says that now he has enrolled in NRC there is nowhere else he actually wants to go: “I desire only to remain at Malleus’s side.”
When asked to describe a time that he was grateful he could use magic Sebek responds, “WHEN I WAS ACCEPTED INTO NIGHT RAVEN COLLEGE!!! That is what ensured I would get to gaze upon Malleus’s noble visage regularly. Any other answer is unthinkable!”
Twisted Wonderland Reference Note 