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A Family Court ruling has invoked warnings to married men and women having extra-marital affairs that they could be liable for lover's claims for up to half their property if the relationship ends.
The 2006 decision, made public last week, threw out a claim by the long-term mistress of a married New Zealander for a share of his matrimonial property. However, family law experts say it was a "knife-edge" decision, and highlights the potential for future claims by jilted lovers.
The case was one of the first to test new "contemporaneous relationship" provisions of relationship property laws, which set out guidelines for the division of property where there is more than one relationship.
The lover has to prove the relationship is more than an affair, and amounts to a de facto relationship.
The Sunday Star Times reported that the case involved Mr B, who had a 20-year relationship with Ms A while still married and raising children.
For much of that time, Ms A lived just 50m away from Mr B's family home, allowing Mr B to go back and forth between the two properties.
His wife became aware of the relationship but "chose not to inquire into it".
Ms A and Mr B were increasingly seen as "a couple" by their social circle. Ms A accompanied Mr B and his children on a five-week holiday.
The pair discussed spending their future together. However, Ms A told the court Mr B kept "shifting the goal posts" and finding excuses not to live together or marry her.
Mr B said in later years Ms A had "built a fantasy" he did not share.
Their relationship ended in 2002, and Mr B remained married.
Judge Smith said although Ms A had a "desperate wish" for the couple to ultimately be more than long-term lovers, that had not happened.
"Their relationship, once beautiful, poetic, intense and passionate, fulfilling intellectually, physically and emotionally to them for so long, nevertheless had never transformed into a de facto one," the judge said. Ms A's claim was undermined by the fact she and Mr B had not lived together, there was no evidence of any financial commitment or pooling of resources, and their relationship had dwindled to a "highly tenuous" state by the time the new property laws took effect in February 2002.
Family law expert Professor Mark Henaghan of Otago University said the decision could have gone either way.
"For Ms A, she's given up her life for him. She had her whole life on hold for over 20 years. From his point of view, he might have promised it, but he never did move in with her. Mr B had his cake and ate it, too, to some extent."
Mr Henaghan said courts had yet to establish what share of property a lover might be able to claim in the event of a relationship breakdown, but it could range from a quarter to a half.
If there was a child as a result of the affair, that would strengthen the chances of the relationship being seen as a de facto relationship.
- NZPA