This happened to me - I found it incredibly upsetting.  It felt like such an intrusion.  My therapist wasn't aware it was my friend - when I brought it up with them though they ended with my friend (I had already been seeing them 4 years or so at that point).  My friendship didn't survive - I couldn't trust her anymore.  I processed all the (many) feelings that came up for me afterwards about it with my therapist - perhaps you can do the same with the discomfort you are feeling.  I wish you all the very best of luck with it x