A new legal definition of "spouse" came into effect in B.C. on Monday, meaning that common-law couples that have lived together for two years have the same rights and responsiblities as married couples.

Under the act, a spousal relationship begins either the day a couple is married, or on the day they move in together — whichever comes first. And once an unmarried couple spends two years living together, it's a done deal.

Family lawyer Grace Choi says it was time for the old family law act to get a makeover.

"Because the Family Relations Act is now about 34 years old, the [new] Family Law Act wanted to ... reflect more about what was going on in society," Choi she told CBC News.

B.C.'s Family Law Act

3 (1) A person is a spouse for the purposes of this Act if the person

(a) is married to another person, or

(b) has lived with another person in a marriage-like relationship, and

(i) has done so for a continuous period of at least 2 years, or

(ii) except in Parts 5 [Property Division] and 6 [Pension Division], has a child with the other person.

(2) A spouse includes a former spouse.

(3) A relationship between spouses begins on the earlier of the following:

(a) the date on which they began to live together in a marriage-like relationship;

(b) the date of their marriage.

(Source: Family Law Act)

The new stipulations under B.C.'s Family Law Act treat common law couples the same as married couples for purposes of property division if they split up.

Couples who have been living together for two years share the same legal rights as married couples, including a 50/50 split of shared debts and assets, excluding pre-relationship property, inheritances and gifts. In the past, people who had been living together for decades were not entitled to share in assets accrued during the relationship.

"If you're the person who owns the assets and decided that you didn't want to get married — part of the reason was because you didn't want to opt into the property division regime — you're going to find this difficult to swallow," Choi said.

In B.C., there were more than 160,000 common law couples in 2011, and that number was growing at a rate three times faster than the number of married couples. Statistics Canada estimated that the number of common law couples across the country was growing four times faster than the number of marriages.

Some family lawyers have advised common-law couples to enter into legally binding co-habitation agreements to save additional grief during a potential future breakup.

Not common across Canada

Though other provinces have some form of marriage-like designation for common law couples, the definitions and rights afforded those couples vary widely.

B.C. family lawyer Grace Choi says the new Family Law Act gives common law couples more rights over shared property.B.C. family lawyer Grace Choi says the new Family Law Act gives common law couples more rights over shared property. (CBC)

In Nova Scotia, a common law ex-partner would be entitled to spousal support and a portion of pension benefits, but wouldn't be able to claim half of any property, including the family home, the car, or jewelry.

Under existing Quebec law, partners in a de facto relationship have no rights, duties and responsibilities to each other — no matter how many years they've lived together.

The Quebec law was recently challenged by the ex-partner of a business tycoon who sought a $50-million lump sum separation payment, but in January, the Supreme Court of Canada ruled that the province's civil code is constitutional in its treatment of the financial entitlement of couples who are not legally married and who separate.

Statistics Canada says nearly 1.4 million Quebecers are in what the federal agency calls "common-law" relationships, according to the 2011 census, and about 60 per cent of children are born to such unmarried couples.

With files from the CBC's Justine Ma and Jesara Sinclair