i think that your therapist might be onto something with his suggestion of it being a boundary thing.

as we grow up we need our own space so we can develop our own individual identity.

skin touching skin can feel very intimate.

when desired it can feel wonderful. when undesired it can feel invasive.

it could have been about fear of merger. fear that you didn't have a self, your own identity. you didn't have your own space. that when she touched you somehow you dissolved into her. that you didn't have your own existence at all.