Mistakes? Lots, I'm sure. Thing is about mistakes, like what did "right", is that sometimes they are only apparent in hindsight.
Such as Mermaid's rant at the OW -- at the time I actually thought it was good, and to tell you the truth still do -- it was honest. I see now that she says that it didn't help anything, but it did seem to be a situation that needed a strong response.
Even RCR says that a b!tc#-mode vent can be useful. It's just permanently staying in b!tc# mode that is harmful.
Of course we can look back and see where we were less than perfect, where something different would have been better. I have "perfect" responses in my head to all sorts of situations, but IRL they just don't come out that way. Well, sometimes they do, but IRL emotions get in the way. We're human.
As for my own mistakes? That would be doing too much "strategy". Doing things in order to get him to do things, rather than for myself. I even told him that I was planning to date. What was most wrong with that was that it was done in order to make him think, rather than because I was done standing. Manipulation never works, and can backfire. That may have set us back ages, as I'm still in this after more than 4 years. That was over 2 years ago, before I ever found RCR's site and way before this forum existed.
I think I did a lot "right" instinctively soon after BD, but I just didn't appreciate how long this takes, and, on the advice of a very pro-marriage counselor, started doing all sorts of "strategies". To give the C the huge credit he is due, a lot were good, and were what is recommended here. The difference was that he didn't accept MLC, nor the time this could take, and as it all went on he got very frustrated with H, as did I.
Which brings me to my other mistake category, which was looking at someone else's "strategy" and trying to apply it wholesale to my own sitch.
And the last thing was how long it took me to learn to look at this as though through a window, or rather look at H that way, and not try to fix everything.
So a lot -- I don't know if I'm still here because of all my mistakes, or if this just takes this long. I think back to my own "early - life" crisis, and really, it's hard to say if I would have gone through it any faster if others around me had done things differently. But I do know that back then I had to go all the way through it all; had I not, I'm sure I would have gone back and made more of a mess at another point.
Oh, and perhaps talking (and writing) a lot is another fault??