Chinese goodbyes come in pairs: the leaver and the host say different things. If you are going, 我先走了 announces it and 慢走 is what you hear back - literally "walk slowly", meaning take care. 别送了 is the polite refusal of an escort to the door, and refusing it once before giving in is part of the ritual. 拜拜 is borrowed from English and is fine among friends.