It all comes down to actions versus words. Life rarely ends like a Disney movie.WAAAYYY late to the party - kinda wished I'd posted months ago (when I first read through your story), but I doubt it would have changed anything.
I'll preface what I'm going to say with this: you are/were more than justified in all of the actions that you took, and in no way am I judging or suggesting that you were "wrong". As in any experience, you had choices to make, and there were alternate paths.
That being said, and obviously I only have the information and experiences you have conveyed to us on here (which is only part of the story) - this could easily have been a case of a badly understood day turning into a self-fulfilling prophecy.
The funeral and surrounding public occasions, while CERTAINLY not pleasant or acceptable from your perspective, from this vantage point meant nothing. You've evidenced significant jealousy (again, not a judgment, I'm a VERY jealous person) - and that could have been why you equated her actions those days to something entirely not there (rekindling things with EX). Then you basically stormed off after limited attempts at conveying your problem with the situation - all but forcing them back together. She was particularly vulnerable and needing support in that moment - again, not an excuse for how she treated you that day, but the follow on issues were you "reading" into the situation, not based on clearly communication (from either of you). Then you just disappeared.
From her perspective, she needed some support and to work through things where she wasn't giving you all of her attention, and you immediately bailed. Then when you ghosted her, the guy that was there got her attention and she decided to see if it could be rekindled - again, maybe I've got timelines mixed up but that's one potential interpretation. That you use this experience, and your first wife, to paint all potential future relationships in the same light also makes me question if the perception you have is colored by reality or by biases in your perspective.
Consider, like many of these "dates/ONS" situations, what you "lost" by having that relationship with her? What was the negative? A few fights here and there, one REALLY uncomfortable day, and in the end feeling rejected (which you kind of forced upon yourself)? Obviously those things suck in the micro view, but there was lots of positives, too. It sounds like you spent a significant amount of time stewing about what could have been and what happened - and so has she. Maybe if that energy got spent on communicating before, and being open and up front about what the issues were and what those issues looked like or meant to each person, relying on what those people say and do instead of trying to "interpret" what they mean, it could have had a different outcome.
Maybe you just like avoiding drama and that's all you see coming out of it, but what, really, does it hurt to hear someone out? So what if she tries to be manipulative? Then she's just exactly where you think she is? Maybe she says or does something that suggests your interpretations were wrong? Maybe she just apologizes. Or, obviously, maybe it's just the ****show you think it was going to be... but so? In the end, you cared, and your biggest pain seems to come from believing she didn't. I think thus far it's clear she did, at least to some degree.
I like that you recognize you don't need a relationship to be happy and healthy. You don't also need to be single and free to be happy and healthy. Everyone has their baggage (including you), so being around others comes with an expectation that at some point, you'll be exposed to that baggage. Don't pre-emptively judge everyone else's.
Again, I hope you don't find this to be insulting or demeaning. Just food for thought. There were 2 people in this relationship, both fully human and with faults. You handled it fine, but I'm questioning if you got the outcome you truly wanted, and if handling it a different way may have gotten you to a different outcome.
I wish health and happiness on you!