You do not have to make oath

"You do not have to make an oath that you won't betray me. But I will make an oath to you: If you try to kill me or one of my comrades, I will kill you. Again. Just remember the scar on your chest which proves your first journey to Kelemvor's realm. And trust me when I say, this time I will make sure, that you definetly won't come back."