If after 10 years, you are still having doubts, the act of getting married will not relieve them. I agree with the previous two posters that sharing your feeling with your GF would be a great start. It does seems as if you love and care for your GF but not in the way you would love and care for a spouse. From that genuine place of love, could you consider letting her go so that she can find someone who does love her enough to want to marry and build a life with her?