AP Herbert, noted 1930s divorce law reformer and novelist, who once gave a parliamentary speech in rhyme, wrote a novel about the 1923 Matrimonial Causes Act entitled Holy Deadlock. Its extremely narrow terms - adultery only, readers of interwar fiction may recollect the 'put-up adultery in hotels' thing in order to obtain freedom from unwanted matrimonial shackles - were not widened, in spite of the recommendations of the 1912 Royal Commission on Marriage and Divorce, until Herbert's own 1937 Act, which finally brought in cruelty, desertion for more than 7 years, and insanity as grounds for dissolution, rather than separation. (It still, however, could not get rid of the guilty/innocent party dynamic, alas.)
I am strongly of the opinion that many people who write on the Victorian era - not just novelists, alas - are insufficiently acquainted with how late these changes came about and how very restrictive the terms of the 1857 Matrimonial Causes Act were.
Okay, it opened up divorce to people who were not in a position to undertake the fanfaraw of a) getting a separation decree in the ecclesiastical courts b) bringing an action for criminal conversation against the wife's seducer c) obtaining a private act of parliament dissolving their marriage.
However, although husbands were entitled to divorce their wives for a single act of adultery - or in the case discussed in Kate Summerscale's Mrs Robinson's Disgrace, a possible sexual fantasy of adultery recorded in her diary - wives could not divorce their husbands except for adultery plus. Plus cruelty, or desertion, or having been convicted of a major sexual offence, e.g. sodomy. Even under these conditions, women did obtain divorces. Some may even have been covertly collusive - there came to be the convention that if a husband left a wife, and she petitioned for restitution of conjugal rights, and he failed to return to the matrimonial home, this counted as desertion. If there was another woman in the picture, bingo.
There were also judges who began to bring in a nuanced understanding of what constituted cruelty in marriage, including the 'wilful communication of a loathsome disease'.
Nonetheless, there were marriages, 1857-1923, which were massively toxic but not rising to the condition where courts would grant a divorce.
We may instance the case of Frank Russell, 2nd Earl Russell. He was the son of that Lord Amberley who once lost a parliamentary election for the scandal over his promotion of 'preventive restrainst', i.e. birth control, and his wife, that Lady Amberley whom Queen Victoria thought should be 'well whipped' for promoting women's rights. He was the elder brother of Bertrand Russell, who also had some colourful days in the matrimonial courts.
Anyway, his first marriage quite rapidly went pear-shaped, with his wife alleging unreasonable behaviour amounting to cruelty and hinting at 'unnatural desires'. In 1900 Frank Russell went to the USA, established residence in Nevada, obtained a divorce there and remarried.
He then returned to the UK and was tried by his peers, i.e. in the House of Lords, for bigamy, US divorces not being recognised in English law, and actually did time for it.
This marriage also broke up, and he then married Elizabeth von Arnim, a marriage which also went bad very quickly - it is said to have provided her with the material for her novel Vera which is not in the least about whimsying around gardens.
Anyway, the state of the divorce law was a major reason why bigamy was such a thing during that period - see Ginger Frost's Living in Sin: Cohabiting as Husband and Wife in Nineteenth-Century England (2011).
The general state of the law at the period is not hard to discover, although some of the more detailed studies of how it played out in the courtrooms is more difficult to come by: some of the best work is by a specific scholar who has been said for years to be producing a massive study of the topic, but so far all we have had is articles and chapters in edited collections, good though those are.