Dear OBB readers: I'm not physically attracted to my man

From a female OBB reader

I have been in a relationship with my man for about 18 months. When I first met him, I never thought anything would come off it. I typically brushed him aside and never gave him too much thought as he is very physically different than what I am usually attracted to in a man. With time, I slowly realized that his character and personality is everything I have ever hoped, dreamed and fantasized about. No kidding. I decided to give us a chance. It has been 18 months now and he has started talking about long term plans i.e getting married. The problem is, whenever I meet or come across anyone with the physical attributes I am attracted to, I start to second guess the whole relationship as I sometimes lust after people who possess these physical attributes. I really can’t help it. I do not want to cheat on this man if we eventually get married but I fear this may happen. I really love this man but this is too confusing. Has anyone ever experienced this dilemma? How did you handle it? How much does physical appearance play in the long run (i.e after you are married)? Reasonable responses please.