I appreciate you sharing your problems with intimacy with us here at Psych Central. It seems as if this reaction has been part of your personality make-up for a long time. I have three suggestions, and depending on where you think you could jump in, you can take advantage of one, two — or all of them.
First, I would find the therapist trained in cognitive behavioral therapy, CBT. This form of therapy — when done individually — can be very effective in helping you learn how to challenge your thinking. Anticipating your own reactions, combined with the consequences, have developed a thinking pattern. A CBT trained therapist can help you undo this.
The second recommendation I have is to immerse yourself in a class where you’re learning something new you’re interested in. Learning something new — with new people gives you the advantage of interacting and connecting, but all under the umbrella of developing a new skill. This can be a way for you to meet new people in a safe environment with a common goal. This often helps.
Finally, the most direct way to deal with this is in group therapy. It might take you a while to find a group therapist, but a group does two things simultaneously. First is a direct challenge to your inhibition, and secondly the group can support and help your transformation.