Maria,
Welcome to SR. I'm glad you've found a site that you feel comfortable posting on, I have spent alot of time reading other posts and the stickies at the top.
I am not in a relationship with an addict, it is my son that brought me to SR, so do not have that sort of background, but . . . that being said . . .
I did feel very strongly, while reading your post, that you seem to 'feel' and 'know' alot about your boyfriend and his therapist. I wondered, are you spending as much time focusing on yourself as you are on them?
If you confront your boyfriend with what you are feeling about him and his relationship with his therapist it will most likely end in a fight and perhaps the two of you breaking up...if you don't confront him about what does sound like a very strange relationship between them, can you go on with your relationship with him...it doesn't sound like it. Maybe it is just time to end the relationship, focus on yourself and finding a healthier relationship. IMHO - in my humble opinion.
Good luck Maria with whatever happens. Others will be along with their replies.