You assumed I'm not. What if I really was evil all the time, huh? What would you have done then? You already swore your life to protect me, you can't take that kind of promise back!!

[Saying that he can't find a different roommate because they're supposed to be buddied up is totally the same thing, right.]

Just ask Saihara-chan! I stole his heart, so now he's loyal to me forever! He'd die for me! Are you prepared to die for me, Aziraphale-chan?!