Discussing this with FIL is tricky. Be open, be honest but don't reveal everything and definitely don't use him as indirect messenger to W. That could backfire as she could feel ganged up on. If so she will fight her corner like a trapped rat.
Plus one concept in DB is making the WAS believe you are moving on without them. So messages indicating an open door counter that.
What you said is not wrong, just may not be strictly DBing.
I imagine my FIL will jump into fix it mode if ever he hears about us. I get on well with him and could talk to him. I don't think I will though. I probably would only say that W has thought about this for a long time and I respect her choice. I may add that I have been hurt but now I just want to move forward and ensure my sons are the least affected possible.
It is hard to know what to say. Don't dwell on this. You are doing well.
Get through the next two weeks as best you can and in the new year I want to read about your aims, goals and actions planned going forward.
Best wishes
R 25 years M 14 years S11 & S13 Working on it alone since Oct 2014 M in trouble a lot earlier (~2 years) Feb 2016. 1st R chat in a yr. Next R chat Aug'17 Still together
