Stuck between a hard place and the biggest rock.

[MrBond]

"apart from calling me arrogant, what are the practical steps I must take in my situation to improve things?"

That's the point. Everyone has been telling you what to do, but underlining all of that is your ego. As a man you feel like you need a "step by step" strategy and EXACT actions. No one can give you that because each situation and person is different. YOU are going to have to figure out a way to stop being arrogant and that means deep meaningful change.

"I also did his exercice, of listing all the ways I have offended and been negligent to my W. This is powerful, because it causes me to see the R in a new way."

Obviously not powerful enough because you went right back to condemning your W just a few hours ago.

"Also, it makes me communicate differently, putting the emphasis on W's emotionnal needs, on her hurt rather than mine."

We haven't seen that. You still are focused on YOUR hurt and not hers. You are still critical of her and her family.

"Having said that, I'm not a machine, and as much as I want to detach and not pity me, I hurt too."

Then do something about it.

"I am impatient and want to see results, which is difficult to refrain. Here's all the difficulty I suppose."

Yes.

I would suggest Skyping her for the purpose of seeing your son and talking with him. Set up EXACT times and dates and stick to them. Don't show her that you'll neglect your son.