travelluvr... what you say is "I have something important to talk to you about but I'm scared because I don't want it to change the good relationship that we have but I feel I need to be honest. Because if I'm not honest it will interfere with our therapy and that is very important to me."

Then you can talk about transference and if you think you have attachment issues you can introduce that into the conversation by saying that maybe you react to him the way you do is because he has become and attachment figure (a secure base) for you and then you can discuss what that means. This can all lead into how you are feeling about him seeing your friend. It's almost like if you have some parental feelings for him she is like a sibling trying to take your parent's attention away from you. We all want to be special to our T's and it's hard enough with the other patients nevermind one that is a friend.

Good luck tomorrow.
TN