Character meme here.
╳ How would they react to seeing a loved one become possessed?
Sebastian would know straight away you were possessed, so none of that “The demon is making me say I don’t love you” stuff. He would seek not to harm you, but because he’s a demon, I’m not sure he could perform the traditional ways of an exorcism. He may possess you back, so you would have two demonic spirits fighting each other inside your body (that sounded better in my head). His reaction would be to force the demon out of you, and proceed to kill him.