Having read the appeal judgement, and its quotations of the original decision, it may be worth inverting the question: why does Mrs. Owens want the divorce?
Perhaps there are reasonable grounds that we can't see, but the problem seems to be that her standards for what counts as "unreasonable behaviour" are rather lower than other people might set them. To be precise, the judgement focuses on four of the 27 examples she offered of unreasonable behaviour, which include an evening out at a pub when they ate together but barely talked. Mr. Owens' defence is that he was simply tired after a hard day's work in the garden. Given that this is the *only* such example she provided of a quiet night out, I think the judge -- and, for that matter, anyone else -- might accept Mr. Owens' explanation, and if anyone else found themselves tired of an evening they'd be fairly unimpressed to find this cited as grounds for divorce.
Another example she cited concerns a conversation about a letter. He called her, asking if he should open said letter, she said that he probably shouldn't, and apparently he pointedly remarked that, unlike her, he had "nothing to hide". This upset her; that this was going on at the same time she was having an affair, and he was getting suspicious, suddenly makes that snarky remark understandable.
All of this is, perhaps, by the by, but when you read the judgement it's difficult not to have some sympathy for the husband's position: he's defending himself against the allegations of unreasonable behaviour, because he doesn't remotely agree that the behaviour was unreasonable.
It will be interesting to see how the Supreme Court rules on this, all the same. My suspicion is that they will come down on the husband's side, with the caveat that maybe the law is broken. But how to change it? Is there a way to implement a "no-fault" divorce law, in such a way that makes it impossible, or at least impractical, for either party to break a contract on a whim?
Perhaps it's out of character for me to take this position, but then again I've only just read the judgement and I guess it's fresh in my head (in particular, in its repeated references to the wife's allegations of unreasonable behaviour being based on "flimsy" and "anodyne" examples.) Every couple fights. I'm just home from a dinner with my Mum and Dad, when we had a lively and passionate, and at times heated argument*, Mum and Dad being on opposite sides. I think we would all be horrified to find that cited as an example of "unreasonable behaviour". Before that we enjoyed a lovely walk; afterwards, it was all forgotten in a matter of seconds. And there are at least 26 other examples I can draw on.
*No, I'm not telling you what we were arguing about.