Good friend or significant other of a nonreligious person.
People with religion can have something to believe in, think that angels are watching over them.
For those who don't have that, and earth angel is simply someone to believe in.
You find everything about them beautiful, from the sound of thier laughter to thier every mannerism, though to someone else they seem completely averdage. It's someone you trust, and can't imagine being without. Someone who understands your mind.