Compersion is not required
Other folks have focused in on what I perceive to be the root of the problems - the need to heal the marriage. Lots of good advice there - I hope both of you take it to heart.
I wanted to talk about compersion. I don't feel compersion. The closest I've come is that I know my partner's other partners make him happy and I accept that. But I have never felt the warm fuzzies some people describe. And that is is ok. Compersion is not a requirement to be poly. Not every poly person experiences compersion. It's not a goal to be achieved. It's not a failure if one doesn't feel compersion. It's a lovely benefit to being poly if it happens. But it's not a personal self-growth goal or an indication that one's personal work to be in a healthy poly relationship is done.