De facto relationships are ordinarily considered de facto when the relationship is registered with Births, Deaths and Marriages, or the couple share a child together, or they've been living together for two years.
The shorter a relationship is, however, the more likely the court is to simply order that each party retain the assets they had at commencing the relationship, so it's not necessarily a case of being in a relationship for two years and then being entitled to, or losing, half the house that you or the other owned before you met.
Hope this helps.