You can't promise that.

( even if he is wrapping around damian and trying to be reassuring. he can't promise it, because, )

You'll do what Grayson did and sacrifice yourself trying to save others. You'll die, or you'll disappear, or get thrown back through time. You will hurt yourself repeatedly to avoid anyone else getting harmed. You'll leave if you think it will help. If your departure would lessen harm or risk for someone else. You already told me to go once.