A financial director's attempt at a quick divorce was rebuffed in court despite claims that his wife of more than three decades had behaved unreasonably.

The 59-year-old man had blamed his wife for the breakdown in their marriage, saying she had less time for him after becoming a devout Buddhist and strict vegetarian.

But in judgment grounds earlier this month, District Judge Cheryl Koh told him he has to wait out the mandatory separation period to obtain the formal split.

She said at issue in the case was whether her conduct "should be construed as unreasonable when it is the husband who has impregnated a younger woman and wished to extricate himself out of the marriage immediately".

The man did not deny his affair with the woman, who is from Shanghai, but said the relationship started in 2010, after his marriage with his 57-year-old financial controller wife had deteriorated.

Judge Koh ruled there was to be no quick divorce.

"The husband ultimately owed it to his wife of 35 years and mother of his three adult children to wait out the three or four years' separation required by law for a divorce on a no-fault basis, instead of blaming her for the breakdown of the marriage," she said.

The man had filed for divorce in December 2016 on grounds that his wife had become "overly engrossed with practising her Buddhist religion to the extent that she has neglected the husband's feelings and needs", among other things.

The wife, defended by lawyer N. Vijay Kumar, countered that she and her husband were both Buddhists, and the religious sessions for her and her children were beneficial and positive.

The wife added that he was hardly at home and returned home late most of the time, especially after 2014, when she said he became involved with his mistress.

The couple have known each other since childhood and pursued their university education in New Zealand. They were married there in May 1982.

Judge Koh was not convinced by the husband's claims, ruling that it was not unreasonable for a spouse to continue to practise religious beliefs just because "the other spouse did not believe or practise to the same extent". The husband had participated in the activities with the family at a religious centre in 2006, but stopped in 2010.

Judge Koh noted that the Shanghai woman had come to Singapore with her own spouse and child, but when she later became pregnant with the plaintiff's child, the hospital called her husband by mistake.

Judge Koh said it must be "extremely trying" for the husband to start a new family again with his expectant girlfriend and is "yet unable to extricate himself from the perceived shackles of his unwanted marriage".

But she stressed that divorce laws are meant to safeguard the sanctity of the institution of marriage as a cornerstone of Singapore society.

"If a spouse decided one day that he wished to move on with a third party, it did not mean that the spouse could abuse the court system by suddenly recalling all the alleged instances of unreasonable behaviour by the other spouse... just so that he could immediately extricate himself out of his marriage."

The husband, represented by lawyer Low Jin Liang, is appealing the case.