Rachel Cusk is a brilliant novelist. I don't think this is her best piece of writing, possibly because she wrote it when she was still desperately distressed - the prose certainly sounds a lot more incoherent than usual.
I don't get the judgemental responses - I think it's an appallingly honest piece of writing (and she's publicising a memoir which is about to come out, hence the fact of this extract appearing in several places - she clearly needs this to sell, as this is her bread and butter, especially if she is continuing to support her ex-husband) in which she bares her own nasty, grieving, unattractive responses to the end of her marriage.
She's not asking for sympathy or stating the facts as in a court case, she's detailing her own irrational, panicked, unlovely feelings. Unfortunately, as in her A Life's Work, she's not being judged as a writer, but as a wife and mother. (And for what it's worth, I'm about to give birth for the first time, and I'm very glad to have read A Life's Work.)
I agree this divorce memoir extract is an unattractive bit of writing - and I did worry about the ethics of the impact on her children - but I also think it's admirable. I have no such experience myself, but I know female friends whose marriages have had to be renegotiated in unexpected ways when they took over the role of breadwinner and their partners/husbands became stay at home fathers.