Is he the right one for me? Is he my "Mr. Right"? Is that just for fairytales???

I have been with my fiance for almost 5 years. We have been engaged for two. He is very insistent on getting married as soon as possible but I am dragging my heels. I am dragging them because we have issues and from that I find myself doubting if he is "the one" for me. He has a good foundation(loving, generous, great to my kids,etc) but we also do not connect on MANY levels. There is a maturity issue and it spills into all areas of our life. I find myself looking at him differently because he comes off a child due to his lack of responsibility and proactive-ness (sp). Unfortunately it affects our sex life or lack there of. I would love for this to work out, we resolve our problems and we live happily ever after but I have my concerns on whether or not this is the situation for me. How do you teach "maturity"?