Could they be hiding behind their "mask" and projecting how they feel about themselves onto you?
It fits with those quotes you just put up Think.
They may well be, but I don't think they know they are doing it.
I think it is all about resentment and blame. They are not happy and they blame it on their spouse (us). If we are unconditionally loving then they feel pain (guilt, unloveable) which they project onto us as blame. If we show them the consequences of their leaving the M, then they feel pain (abandoned, unloveable), which they blame on us.
And in my sitch, I think when I show unconditional love for my W, I think it only feeds her fantasy that this is how it will be during and after the D - that we are smart, civilized people, so, of course, we will be great friends and co-parents despite the D.