I understand that some of what folks are writing may be upsetting to you - different people come at the same issue with their own filters and their own paradigms. They will give you their perspective on it, and you can decide whether it is something to take on-board or not...
The advice I most often give is that folks have to first understand themselves. What are their core beliefs and values? What things absolutely have to be in place in order to be content in life (because we all deserve to be content). Polyamory (the ability to love more than one, freely), honesty, religion, sanctity of marriage vows are some of them. Nobody should tell you what you should believe - only you can know that.
Just a little personal "war story" - I lived from my teenage years up until 12 years ago believing that monogamy was the only "right" way to go, while deep in my core I knew that it should be ok to love more than one. I also believed in honesty as a core value to who I am - I wanted to be seen as trustworthy and know I could trust others around me.
The trouble is, that monogamy/polyamory fight was so strong in me that I started believing that I was a very Bad Person. I stopped caring, and totally lost sight of my core values. I stopped taking care of myself, became depressed, and started doing dishonest things. I hurt the people I was supposed to be caring about the most. I lied about so many things. I also stopped caring at work - why should they want me?
It was a downward spiral that I am most certainly not proud of. The only way it ended was for me to reject monogamy for myself and really go back to working on what I cared about - which was honesty. The principles of polyamory - responsible, honest, open caring relationships - appealed to all of my core values and I realised that the only way I was going to live up to them was to take monogamy out of the picture and if that made me an evil person in someone else's eyes, so be it - I could at least start to live by a set of values I believed in.
My partner of several years believed that our relationship was at an end. I don't think she really understood why - I certainly wasn't in a position to educate her, with my own head being a jumble of self-hatred and loathing. She was a huge help once I started making my breakthrough - she believed at the time that she was doing it as a friend and that it would mean the end of us, but she cared about me enough to help me through. She knew in her heart that she was most definitely monogamous. So much of what I was saying while talking about my thoughts made no sense to her, but she listened, and questioned and helped me to find that inner "me" again.
It took me about 10 years to truly rebuild and put the crap that I had built for myself behind me. It wasn't easy, but over time, things have got far more stable. Those core values have become embedded again and I live my life according to those values. I will not compromise them again.
If understand where you are coming from, you have a fight going on inside you right now, trying to reconcile all the things you feel you should believe with all the things you really do believe. In my opinion, that is the first thing that you should work on - resolve that fight, and put an end to it. Maybe your husband can help, if he is open-minded enough, maybe you have to do this on your own, maybe you could use some professional help to get you the tools you need. I don't know.
But please understand that you have my sympathies and empathy for what you are going through. This stuff is NOT easy.
"Listen, or your tongue will make you deaf." - Native American Proverb