Welcome to the forum.
I'm trying to understand. Do you feel you are genuinely poly or do you feel your wife's possessiveness is driving you away from her and towards a more open relationship? Would you be happy in a monogamous relationship with your wife if she would simply relax and let you make friends, talk openly, or (
) watch porn?
Your wife may or may not be monogamous by nature. (Even mono people are capable of fantasizing every so often, though they wouldn't act on it.) But this is not the problem. The problem seems to be her possessive issue. And that usually comes from a self-esteem problem.
I used to be this way with my husband after alot of damage done to me by men in the past. Also, he was poly in the beginning of our relationship (we both were to an extent) and a two year emotional gutting involving a situation with his ex gf after we went mono severely hurt my trust in him. It took a very long time for us to work things out but we're happy and secure now. Does she have reason to be this insecure in your relationship. Has she been through trauma? Have you yourself done something to destroy the trust?
It sounds like you're nearing the end of your rope with this, but hold on just a minute before making radical life changes. Especially if you truly love her and want a life-long loving relationship. How willing is she to open up completely? Have you tried couple's counseling? There seems to be more underlying issues than just the poly/not poly one.