One thing I am trying to get you to see is your problem with monogamy and honesty. Just because things go a certain way doesn't mean you don't have a problem.
-- It is good that you plan to end your R with 25 y.o. That does not change the fact that she was having a sexual relationship with a married man who she did not know was actively working on trying to reconcile with his W by consulting with therapists and posting multiple times a day on a discussion board. (not "merely having thoughts", again minimizing what is going on...)
-- Great, you didn't miss the anniversary you didn't plan on celebrating. Yet you believed you forgot it and told your W over and over that you didn't forget. You misled her. This counts as lying. It does not matter if you were both mistaken about the facts. You believed one thing and told her the opposite.
-- You often blame external circumstances for your unwise choice.
--You twist what you hear to make it fit what you want to believe. For instance, the problem with the rape thing is not that you don't know all the details. It is that W told you she was raped and you discount, distrust, and minimize her trauma without, evidently, having any reason to do so.
-- You fail to treat the women in your life as though you respect or value them. Until you respect and value them, you will not have a successful relationship. Until you respect and value yourself, you will not respect or value them. To respect and value yourself, you need to work on yourself.
As for your stepson, I would strongly advise you to be sure that you have W's consent before you take her child somewhere when she specifically said she did not want you to do things with them. If someone took my kid in such circumstances, that would end any possibility of reconciliation.
You have been in the kids' lives for only a year as a stepfather and since August as someone their mother plans to divorce. It really is going behind your W's back to ask SS to do something with you. You are bypassing her. That is going behind her back and is inappropriate. And, my guess is that your DB coach was in someway unaware of the dynamic when she suggested you make plans with SS without his mother's consent, and in particular, against her clearly expressed instruction to not do things with her children.
