Scenario
Who paid the mortgage after move-in is not the same question as whether this province treats unmarried partners as spouses for property.
In Ontario, unmarried partners generally do not get Part I equalization. In British Columbia, unmarried spouses can have Part 5 claims after two years or a child. In Québec, family patrimony does not attach to de facto unions.
A clause that says 'the house stays separate' may be surplus, central, or the wrong category depending on that default. The province pack has to lead.
Equalization of net family property in Part I is a married-spouse machine. Unmarried partners do not get that statutory equalization. A cohabitation agreement is how they allocate property by contract. Some support rights can arise after three years of cohabitation or a child of the relationship.
s. 3 treats as spouses persons who are married or who have lived in a marriage-like relationship for a continuous period of at least two years, or who have lived in a marriage-like relationship and have a child together. Unmarried spouses can have Part 5 property claims. That is not Ontario and not Québec.
De facto spouses do not enter family patrimony by cohabiting. Property follows title, ordinary contract, and unjust-enrichment ideas a lawyer may assess—not the married spouses’ family patrimony.