As a mage in a romance with him, if you ask him what he would do if you're possessed he acts very conflicted. Your Quizzy then assumes he would go through with putting her down, but he tells her it's not that simple and he'd rather not think about it. In the past he probably would have, but it's much less clear in this case and it feels like it could go both ways.
However, if he breaks it off with you after you force him back on lyrium (without promising to help him find another way later) and you ask him the same thing, he basically says something like "What do you expect? That I would jeopardize the safety of the Inquisition instead of doing what had to be done?" in a really cold and firm tone of voice. He goes back to being all business, because basically you've told him that his duties come before any personal desires or emotional needs. It was actually a bit shocking when I watched the video of it because I've been so used to him being softspoken towards my Quizzy, hah.