There's an idiom for never being satisfied with what you have and always looking out for something or someone better, particularly in reference to dating. The phrase is something like
Keep one eye on the door
referring to watching the door for the next new hot person to walk in the room.
My google searches have not resulted in any hits, which make me believe that I don't have the wording quite right. Does anyone know what this phrase is supposed to be?
Best Answer
There is a phrase that captures the idea perfectly, although it is not exclusively used for dating: Always chasing rainbows.