A phycologist has told me they think W is playing games. I hadn't thought much about it. However, thinking back, W had been doing a smirk at times when I thought she was telling lies and I'd caught her out, and doing it when it seemed she'd been deliberately trying to start arguments. I have now found there is a name for it called Duper's Delight.
I also noticed that her behaviour can go from very happy to awful within a second like it's all an act. I've also noticed that she acts to get sympathy and attention from others. Her support network is now 3 stubborn single mums.
She has left me, so why the need for doing all that BS?
Regardless, detachment and to rise above it still seems the best policy to me.