Sex acts are /= to intimacy! Your marriage does not lack intimacy because you're not into specific sex acts.
Does it suck if a partner has specific sexual fantasies and their partner isn't into it? Sure. But that is something you have to live with in a closed relationship. People are not dolls for our pleasure.
You should never feel like a bad partner because you don't want to engage in specific sex acts. And honestly, I think anyone who tries to pressure their partner into a sex act they don't want is awfully selfish. How can you not care that your partner doesn't want to do it, and try to persuade them anyway? So gross.
As for compersion..
They mentioned this term several times:
There's actually a word for the joyful feeling that a polyamorous person has when his or her lover or spouse walks through the door after spending the afternoon making love to his or her new girlfriend or boyfriend: compersion. Compersion is such a novel concept that you won't even find the word in the dictionary (unless you look in the Urban dictionary).
I’m guessing this is a fundamental requirement for a poly relationship to be successful. You have already told him that you are monogamous. The above concept doesn’t compute for my brain. Sounds like it would not for you either.
No, compersion isn't a fundamental requirement. Poly people aren't a whole breed apart. We still have to learn to manage emotions, although it's generally encouraged to drill down and sort out your Whys and deal with the root cause, rather than trying to restrict your partner's behaviour. That's assuming your partner is behaving ethically- no one should be trying to deal with their Whys if a partner is breaking agreements! In that case the why for negative feelings is obvious.
But generally, I think most people understand the concept of being happy when their partner is happy. If your partner went out with a friend and had a great time hanging out and came home all smiles, I'm sure you'd be happy for them, right? That's the base idea behind compersion. Not everyone gets to a place where they can be genuinely happy when their partner is dating others, but at the very least, tolerance/neutrality are a must. When new poly people ask for advice on how to manage jealousy or worry about being replaced or anything like that, we encourage them to work on themselves, find time for themselves, and focus on personal growth and development. If you repeatedly get negative emotions when your partner is dating, I think that's a clear sign that you really don't want to be in that kind of relationship at the end of the day. And there's no need to have a relationship style you don't want!
But it really does take time. It's a very, very rare person who is immediately OK with polyamory or open relationships and floods with compersion immediately. That just doesn't happen, especially with societal conditioning. Which is why you really have to want to do this, because you have to be willing to put in the time to work on your communication and emotional management, and to strengthen your existing relationship if there is one (not everyone comes to open relationships while in one, after all). So just because it doesn't immediately warm your heart doesn't mean that it's wrong for you.
Once again- that being said, I don't think it's easy to get to a place where you can have a successful open relationship with a partner who has broken trust. I know a lot of open/poly people, and I know exactly one couple who have been able to rebuild from cheating and transition to an open relationship. But there was genuine remorse and a desire to reconcile, IC and MC with a kink aware therapist, and they still put a ton of limits on their connections to ensure that both partners felt safe. I'm not a big fan of those kind of limitations for a lot of reasons, but I can understand why they felt it was necessary in their case.
Realistically, though... your husband does not sound like someone who is willing to put in the work. Divorce is scary, but you have a much better chance of happiness. Not only do YOU deserve happiness, but your children deserve a happy parent.
When my xWH walked out on us, I thought my world was ending. There are a lot of things in my life that are still bad, but the one thing that isn't is my love life. I've never been happier. But I CHOSE this for myself; no one pressured me into it. If you wouldn't date a brand new person and give an enthusiastic yes to an open relationship, this is not going to make you happy.