I was always poly, emotionally. But I stayed in mono relationships because it was expected. I was a serial monogamist, going from relationship to relationship because no one ever wanted to leave it open. And I often cheated when the feelings for someone else emerged. And then broke off the relationship(s). In my 20s I finally met someone who allowed me to date another man openly but even he couldn't take it after a year of indecision. I felt dirty to be honest. Until my husband (then friend with benefits-because I was never allowed an in between of a serious relationship and a friend) gave me the "poly" title. I fought it for years, stayed mono with him, but the bisexual in me won out and I dated a woman.
I'd rather be hated for who I am than loved for who I am not.