That's a good question, Panda. I hope someone more experienced will come along and answer it. I recall hearing/reading that at BD.........is like a half way point...........not sure exactly. My exH first stated his "unhappiness" began 6 months prior to BD...........but then later he came back and said it really started two years before BD...........and as I went backwards in my mind....the two years fits perfectly. His mom died around the time frame he is speaking of.........so, perhaps it did start that far back. I will soon hit the 4 year mark of all of this......so, I don't get the "half-way" mark regarding the date/time of BD. As my luck goes, my exH will take the longest way out......so, he will probably be in this for the duration......10 years??? Oh, goodness!!
I hope someone else will come along and shed some light on this.