I'm seeing two things to consider.
In terms of telling the other man some things: it makes sense that the fact that you have no kids together does open some doors for your conduct/decisions, that wouldn't be there if you were sharing parenting for many more years -- if a decision crashes and burns, there won't be fallout on the kids. So yeah, you might have some more leeway to consider choices that wouldn't be there in a coparenting situation. I think I'm tracking with you that these are some things you'd consider telling him:
my opinion / what I believe about her...
the real reason I left...
where I am coming from...
what I (he) was getting into...
What do you hope would happen, ideally, if you were to tell him those things -- for him, but importantly, also, for you?
Are you hoping that he will understand your experience and where you are coming from? Are you hoping for something else?
What would be the best case outcome? What would be the worst case outcome?
...
Secondly -- although you don't have kids in the picture, you do have this going on:
we are involved in protracted litigation and are not on speaking terms.
Remind me if you have a lawyer?
What has your lawyer recommended (or required) about you contacting your ex or anyone involved with your ex, while litigation is ongoing?
I would think through, and consult with a legal professional about, if you contacting your ex's partner unsolicited would have an effect on your case.
...
Everyone wants to be really seen, really heard, and really understood, especially by a partner, and when we don't get that, it has an outsize emotional effect on us, that impacts our decision making.
I wonder if you felt unseen, unheard, and not understood during your marriage.
I'm curious if that significant loss is in play here?