I too struggle with boundaries, so it's important that I find friends and significant others who are willing to vocalize their boundaries and understand that my intention is never to hurt them, to just be straight with me when I'm doing something wrong. I wonder if your current relationship would be willing to do that for you if you brought it up?

As far as help defining boundaries, I'm not really sure, but you could try to find a different therapist who maybe specializes in social disorders who may know some tips and tricks that some others might not think of.