To care about someone so much that your happiness doesn't matter anymore - just theirs. There's nothing you won't do for them, you just want them to be happy. They fill you with wonder, you are completely amazed by them. And when you are in love with someone, you'll even let them be with someone else if they can be happier without you. Its a feeling that runs so deep it conquers everything. You're not afraid of anything. All you want is them, and their happiness. They are your number one priority, over yourself and everything you know.
They are your world. And you can only wish to be theirs.
"I am so in love with you so much that I'm leaving you. I can't make you happy. But he can. So go be with him. Cause I'd rather be miserable without you then be with you while you're miserable."