One more thought: if you do start seeing a therapist, and after a few sessions you feel that they are not very poly-friendly or are not giving very poly-friendly advice, don't be afraid to seek out a different therapist.
I wouldn't wait for a few sessions, I would find out before laying down a single dollar. You're within your rights to interview potential therapists before hiring them. If they refuse to interview, walk away. And during the interview, ask them specifically if they are polyamory-friendly. Use the word "polyamory." Whether they know the word will be the first test. Their reaction will be the second test. And a direct question whether they support it will be the final question.
I was also concerned that it was my problem if my therapist wasn't telling me what I wanted to hear. I thought that I had to face uncomfortable truths or something.