Was it always this way? Love is more than skin deep. If he is a nice kind man and you made a commitment to him then you should find the inner beauty. You can attempt to make his outward appearance more attractive or take that inward beauty and try to transform it to his outward appearance.
I would always advise against cheating, but this is an important issue to talk about with him. Maybe encourage him to go to the gym, get a haircut, change his style, whatever it is you hate.