Divorce was sanctioned by a private Act of Parliament pre-1858 making it beyond the means of most people. The House of Lords Record Office and the National Archives hold papers relating to the successful cases.
Couples could go to church (consistory) courts of bishops to seek annulment if they felt one party in the marriage was a bigamist or from 1754, when Hardwicke's Marriage Act had come into force, that they were under the age of 21 and had married without parental consent.
It was then possible for the
husband or wife to apply for a declaration of nullity. This was not a decision
entered into lightly because it rendered any children illegitimate
and it also meant the wife was no longer entitled to a third of her husband's
property when he died. This was known as rights of dower. Records of these
courts are kept at local Record Offices.
Sometimes couples separated unofficially because they could not afford to go through the process of dissolution. If one or other of the parties wanted to remarry they married away from the parish and hoped no one found out they had married bigamously.
Another way of legally separating was a mensa et thoro which was granted if there was evidence of adultery or cruelty. Resources regarding this are held at local Record Offices or at the National Archives.
In some cases, if the woman was adulterous, then the husband sold his wife to her lover in the market. This had no basis in law, but because it was committed publicly it meant the first husband was usually protected from any of his wife's debts.
It also meant it protected the new husband from any action from the original husband. You may be able to find information regarding any sale in quarter session papers or in local newspapers.
For more information about dissolving a marriage before 1858, please peruse the National Archives leaflet Dissolving a Marriage before 1858: further research.
From 1858, it became easier for couples to separate, but women did not gain equal rights with men until 1923. Surviving papers from 1858-1943 are held at the National Archives in Series Reference J77. For more information about divorcements after 1858, please peruse the National Archives leaflet Divorce after 1858: further research.