Things like this are tricky. We have no way of knowing what is pushing people away without knowing more about you. However, I can say there have been issues with people I know in the past who have wanted relationships. Here are a few:
1) Some women have standards that are simply too high - They want a very specific man who probably doesn't exist or, if they exist, they're probably already married to people who saw their potential before they became so.
2) Some women are attractive, funny, sexy and incredibly intimidating to a lot of men. If you're brilliant, sexy, funny and attractive, many men will simply assume you'd have no interest in them. I knew one woman who fit that mold exactly. I felt bad for her, actually.
3) Some people have an awful lot of baggage - Everyone has issues and loving another person for everything they are is part of the package deal. When they no longer have issues but a whole subscription, it's time to back away.
4) Some people are simply aloof. They haven't mastered the art of flirting yet or spotting when someone is flirting. That's fine; Nobody is born inherently with knowledge of what makes the opposite sex tick. You might want to consider getting some help closer to home - There's no shame in it. If this is you, you learned to drive, you learned to ride a bike and you can learn how to read people.
Those are the major things I can think of right now - There are probably a lot more, but it would be best to talk to your best girlfriend or guy friend and ask for honest opinions. Be warned - If you're the type to take offense easily, you probably will not get honest feedback and they'll just say they're confused. If they give no advice, that's a surefire suggestion that they're too scared to give honest feedback. At that point, you'll have to go elsewhere and do some real introspection.