How can i teleport a player to as specific entity

So basically i have this entity that can be ridden that teleport  you to a custom dimension and i would like to make it so that when i leave this dimension it teleports me at the position of this entity. For singleplayer i just have   to use variable to store coordinates but in multiplayer if a play ride the entity away when i am in the dimension it will just teleport me to the place where then entity was when i entered the dimension and not it's actual position.