Adultery is defined as “voluntary sexual intercourse between a married person and a partner of the opposite sex other than the lawful spouse”. A same sex couple will not be able to divorce on this ground, although of course the spouse in a same sex marriage could divorce on the basis of their partner's unreasonable behaviour.
The person applying for the divorce (the Petitioner) needs to show that the person receiving the divorce (the Respondent) has committed adultery and that the Petitioner finds it intolerable to live with the Respondent as a result of this. If the Respondent does not admit adultery in the divorce petition or a separate confession statement then it can often be complicated for the Petitioner to prove this ground, and therefore a petition based on the grounds of unreasonable behaviour is often preferred.
It is worthwhile noting that an individual, if still married, can be found to have committed adultery even if the parties have been separated for a significant length of time and the breakdown of the marriage occurred for a completely separate reason.
If the Respondent has engaged in sexual activity that does not constitute sexual intercourse or has had sexual intercourse with a partner of the same sex, this does not amount to adultery. However, in these cases, a divorce is most likely to be brought by the Petitioner on the grounds of unreasonable behaviour.
Although it may initially seem that issuing a divorce on the grounds of adultery could be construed as a hostile act, an adultery petition can be a simple way of progressing the divorce for all concerned. There is no requirement to name the other party with whom the Respondent committed adultery. Indeed, naming the other party concerned often makes matters more complicated and expensive.
The Petitioner is traditionally entitled to claim the costs of the divorce from the Respondent in adultery cases. It is often the case, however, that because both parties want to progress a divorce quickly and amicably it is agreed that they share the divorce costs equally.