Freewilled, I am sorry that you had an abusive experience in therapy. I don't see, however, that being guarded is really going to protect you against someone who is abusive. People who abuse can use any speck of information against you in order to hurt you, and you likely still would have been hurt if you had said less. You didn't get hurt because you shared too much, you got hurt because of the person you shared it with.

It can be healing to allow yourself to drop your defenses, although it is always a balancing act to have them where you need them. But I think the healthy trick is learning when to lower your defenses and when to raise them, and to not walk through life thinking that everyone is going to hurt you.