Sometimes sexual attraction ignores D/s orientation. I've known couples who were both submissive and dominants who wore the collar of the person they fell in love with. My own boy, @masterofgame, has never identified as a submissive. He was more of a dominant, and a bit of a sadist, when I met him. But he demonstrates his love to me by submitting, serving, and wearing my collar.
Four tantalizing tales explore Who Tops Who when dynamic dominants find each other irresistible. http://www.eroticawriter.net/shortstories.php?coltitle=WhoTopsWho