I can understand feeling and being that way, not because I am the same but because I am the exact opposite. I have experienced the extreme of all the things you are avoiding by being closed off. I totally get it because I have had some pretty horrible things happen to me by and because of people I have trusted and loved. On the other hand, I am experienced some of the most profound moments and created some wonderful memories because of those who love me in return. I guess it all depends on if you are willing to risk pain to find happiness, because life is full of balance and we can't have one without the othe from time to time. We also can't deny that fact if we follow a faith that thrives on that very idea.
Many blessings to you, and maybe someday you will let someone in. I hope that you are happy no matter where life leads you.
