From what I remember the reason it was denied was that she could not prove unreasonable behaviour and in fact it was her adultery and unreasonable behaviour that ended the marriage.
He just refused to accept blame. I have seen loads of women advised to string out divorces and not give their ex what they want.
Personally, if I was him I would start divorce proceedings myself and just get rid. I am sure he is a dick. But it sounds like she is a dick too and should have tried to divorce on proper grounds.
Her reasons for divorce were described as 'flimsy and exaggerated'. And there is this
Mrs Owens' lawyers argued she should not have to prove Mr Owens' behaviour has been "unreasonable", only that she should not "reasonably be expected" to remain with him
Her legal team seems like they are trying to push a no fault divorce through. Which doesn't exist. I think her legal team is taking the piss and will be earning fortunes, for being a bit shit.
I do think a no fault divorce should exist. But it doesn't. The law needs to change.