Myolie and Wong Hei? couple look? I don't know, its pretty subjective. by the time they got married, his character is supposed to be more mature and older looking and stern.
chemistry wise...put it this way, they are always bickering before marriage and even after that, he could not stand her, constantly driving her away. but the ending scene between them was really sweet and sappy.
oh yeah, Hei did not play the lead in romancing HK.