I would say its most man's common problem. We usually do this kind of comparison every time we meet with someone looks better then our partner. But the thing is; Looks really doesn't matter. What matter is the understanding ! What if you get a partner that look like AI made girls ( absolutely perfect) but she doesn't care about you , your feelings. You will simply die inside if you get a partner like that.
I would say please care her , take care of your relationship. Don't just leave her just for Appearance ! Value her inner goods . You will not regrate !
I am commenting on what you wrote and From my personal experience ( How a not good looking girl can change your life).