As others have said, this is NOT poly. This is a dictatorship, and if he feels like he is cheating on her, then they are a monogamous couple.
Maybe you do need to find someone to remind you of what it feels like to be treated like a valuable human being. Odds are though, that unless you start treating yourself like a valuable member,....you`ll attract someone like your husband.
I am sorry this is happening to you. I hope you find the intestinal fortitude it takes to find your way out of such circumstances. My best to you.
Look around the forum and read, read, read.