Where do u draw the line with platonic friendships?

How do u know if your male guy friend is just that a friend or hes being friends cause he wants more. I am friends with a guy in work weve been to lunch twice in work and hes got a gf in uni. I enjoy his company but dont want more. How can u tell where the line is drawn. As he has asked me to the cinema and to look at his new flat so where do u draw the line