Last year an ex-husband's application to end spousal support was denied without a hearing after alleging his ex-wife lived with another man for over a year, purchased a home with him, read a co-parenting book with the other man, and had her children refer to him as their "step-father".
The ex-wife responded that she did not hold out the other man as her spouse, denied referring to him as the step-father, stated that her friend maintains another residence where he gets mail and keeps most of his belongings, that she was not engaged, does not wear a wedding ring, did not file joint tax returns, has her own health insurance and keeps her bank accounts in her name alone. While the facts of the degree of joint occupancy and sharing expenses were partly disputed, it does not appear that she denied purchasing the home together and both residing together for significant periods of time.
Domestic Relations Law 248 ("DRL 248") has always been known by divorce attorneys as notoriously difficult to prove so that a court will end maintenance. Many people have tried based on the ex and new partner living together and most have failed. DRL 248 requires proof that the two person are habitually living together and holding themselves out as husband and wife (emphasis added). In other words, it is not enough to show just the financial and romantic relationship you need much more such as proof that they refer to themselves as Mr. & Mrs. or as husband and wife or utilization of the partner's last name on accounts, or listed under one name in public directories. The fact that there may be joint purchases whether a home, car or furniture by itself will not be enough. The singular fact that the two people live together will not be enough without more under DRL 248.
What many lawyers will suggest when drafting Settlement Agreements is a termination standard different from DRL 248. For example, I would often draft as a terminating event if the ex-spouse is living together with a person unrelated by blood or marriage for a period of 30 consecutive days or for 60 non-consecutive days in any 12 month period (or some variation of duration). This way if a couple lives together for 28 days and then one goes to a hotel for two days you can still count total days over months rather than have it defeated by the brief absence within one month. I have also drafted clauses that refer to living with another person in an "intimate relationship" and "sharing financial expenses together". So if the couple shares utility bills, rent or mortgage payments, there is a way to show economic dependence. A person renting within the home and not in an intimate relationship would not end spousal support.
The other difficulty is that a person is not compelled to agree to other language as suggested to lessen the burden of proving a terminating event(s). So often in negotiations the recipient spouse will not agree to the non-DRL 248 language. Thus it is a product of negotiations. For example, a child support paying spouse does not have to pay child support beyond age 21 (absent certain situations) and therefore if a recipient parent wants child support to age 22 if the child is a full time college student, the maintenance clause could be negotiated. Other economic benefits can also be traded for the spousal termination language desired. Almost anything that you can think of can be used for the negotiations.
The best way to reach an agreement on this complicated issue is to have a skilled and experienced matrimonial attorney at your side and representing your interests.