Not wanting to be on this boat........

[Buffet]

nothing major new to report here, W is going around acting like everything is "normal" Her sister is in town and staying with us which is comical b/c she knows everything is not normal but the W insists on acting life life is good no problems. She wants us to go out to dinner together and makes plans for the weekend. Than in a moment when it becomes just me and her she just gives me this "death stare" like she truly hates me it feel?? I really do not understand what is going thru her head.
Another more direct question that maybe I can get some advice on--W claims that she has been unhappy since more or less the birth of our son who is now 2. She was on meds for post partem but stopped taking them. Now I have also had some issues during these 2 years with my fathers death, and job, and home changes. She claims to have gutted it out the last 2 years waiting for me to snap out of it. Well we went on a big trip to Hawaii in March and it just went Ok---It was for my work so it was not truly a vacation away from everything. When we got back at the end of March I really started to analyze where I was in life and what i wanted the rest of life and marriage to look like. I realized that I was not happy, had not been happy and actively started to make changes (diet, exercise, hours spent working, family time, re-commit to my marriage, etc..)
I decided to do this and largely keep quiet about it, I wanted to prove to her and myself that this was truly a life changing decision for me, not a temporary promise that I would not hold up. This went on for about 4 months or so. Starting in August I noticed that my W had really pulled back way more than even before. Our sex life had dwindled from infrequent to none, and now I noticed she would not even kiss, cuddle, show any affection at all.
SO than I started to talk to her and got the ILYBNILWY speech and that she claims that after Hawaii she was just thru with everyt6hing. I told her about the changes that I had silently been implementing in my life since we had gotten back. She commented that she noticed these changes but did not care, or did not think that they were genuine, and to little to late.
So, my question is why did she hang in the relationship until say March but than in late March when she gets what she was asking for all along it is no longer good enough??
Also, why hang in there all this time to get it and than reject it? Why did she not just leave or file D either 2 years ago when she felt this way, or anytime along the way, or especially now that she claims this is too little to late and her love for me is gone?
Sorry this is long winded but I think that if I could get my head around this I would have a much clearer picture of how to go about this and what I want to do with my life going forward. Is this a lost cause? Can it really be to little to late by missing each other literally by the time of a plane ride?