Well it possibly might be tied to simply something new. We're all scared of doing new things and especially letting ourselves be vulnerable both physically and emotionally. So in that case I think the importance is in finding a partner to whom you have an emotional connection and can make you feel comfortable when you let your guard down.
Is there anything in your past that might have led to the fear of intimacy? Maybe something bad like assault or even mild like abandonment issues from a divorce? Those things can make getting close to someone difficult as well and are best discussed with a counselor.
Finally, no, you're not alone. A quick scan of this forum and you'll see there are plenty of people just like you.