Marry, just because you have low self-esteem, is the worst kind of mistake you can make. Even if the girl is "nice", it's not enough to ruin your life. Look at how many people married their "dream girl" and are unhappy. If it is not "THE GIRL" then you are committing a huge mistake.
If being single is a problem for someone under 40, then you should contact your psychologist. Even if you are not good with girls, you should still be comfortable being on your own. For me, this kind of fear could mean depression.