What is the manga called about a girl who falls in love with guy who lives in her attic she works in a flower shop and she becomes a secretary to be with him as she is of different social standing?

I think you're talking about Kiss/Hug. Ryuu and Yukino meet at a festival and he declares "you will be mine." She works in her family's flower shop, he is rich and she is, well... not. He stays in her attic. Hope it helped....