Okay I know some people think this as Chaol betraying Aelin, but Aelin is kinda unpredictable at times. He knows what she can do and is hesitant to say that he absolutely knows what she is up to, because in a way he can't, often no one can. And this swearing upon Yrenes life is weird to me. They make it sound like Hasar going on like'Tehee, we like you girl, but if we found out that he was wrong about this we are gonna execute you on the spot.'