Just my opinion (and OP, you may have already resolved this; I see it's an older thread), if a counselor is being that vehement about their personal views with a client, that's a problem. Regardless of a counselor's *personal* opinion of a subject, they should be an objective listener and not make judgments during sessions. That's counterproductive (and, again just my opinion, unethical). People are going to judge, but a counselor should keep those judgments to themself when working with a client.
That said, it may be a case of your counselor just not knowing enough about polyamory. Maybe some education would change her mind. And it sounds like you're going through a time when you need a professional you can trust, so if you trust her despite her opposition to polyamory and her apparent need to state it, then definitely stick with her.
It really stinks that you had such a horrible experience with your ex. You have no clue who I am, but I hope you don't mind me sending you positive thoughts for healing as you go through your divorce and build your new life. (I've been there...)
I was fortunate with my counselor. Last year when Hubby and I opened our marriage, rather than giving me all the reasons it wouldn't work and how opening a marriage can destroy it, etc.--all things I heard from the "swinger" site Hubby and I met through--my counselor actually praised me for finding a solution to the sexual incompatibility Hubby and I were dealing with. And when I told my counselor about my relationship with Guy several months later, she said she was glad I had two men in my life to love and support me.