I am 6'1, and I have dated someone shorter than me. I am not discouraging girls that are in relationships like this; however I do have a personal vow that I would prefer if my mate were if not my same height, taller than me.
I'm 5'11.5" and once dated a guy who was 5'8" and it worked fine however if it really does bug you inthink theres a point where sexual attraction can be lost due to insecurities which is a shame but can happen.