333 Not trying to be a jerk, just providing some feedback based on what I've seen.
That being said, I don't know you personally, and only know of you what I can interpret from your posts.
My thing is that I haven't seen a lot of introspection on your part about your mistakes in the M. I do realize that you left him first which probably means there were things you just weren't happy with. That's understandable. I'm sure he has his flaws.
Yet as an LBS that almost turned WAS myself my W leaving opened up my eyes to a lot of things I didn't like about her. Things I have demanded she change, and she has. We are still struggling, but we actually have genuinely happy days together.
DB has to me always been about working on yourself to be the type of person who a spouse would be crazy to leave. Are you becoming that person?
I have noticed you have tried detaching and other techniques. Yes they are effective, but largely counterproductive if you are not working on yourself. I get the impression that a lot of your detachment comes more from anger, frustration, and the need to get back at him, than what it really should be which is an understanding that you need to make yourself happy first, and you detach from people when their actions show that they have no consideration for your feelings.
The little incident with each of you trying to serve each other first sounds more like you two are more concerned with your pride than actually saving a relationship and a family.
Like I said not trying to be a jerk just some things that have stuck out to me.