separate yourself from him for about 3 days to a week. While your apart (no contact, not even text or phone) picture his face while you are apart and find things in his face that were not as perfect as you had thought they were. Even the smallest thing, like maybe a mole or a freckle in a certain place. Then say to yourself, 'hmm I don't know why I thought he was so perfect, because he is not'. Then let it go and try to put him out of your mind and concentrate on something else, whether it be a movie, cleaning house or exercising. Do this 3 or 4 times a day.
Then when you see him again notice the point of focus, but not for long, don't make it obvious, then try to see something else that is not perfect. Stay apart for a couple more days again recall those points about him that are not perfect as you did before, 3 or 4 times a day. Next time you see him, you should begin to see him more as a friendship.
I actually used this method with a married guy who was one of those guys that you take a first look and instantly fall in love. He is really a nice guy and he eyes twinkled when we talked, and I just felt something really click, but I knew inside that he was married and things just could not be more than friendship. And it worked.