I’m 36 and have been with my current girlfriend for almost 5 years now - my longest relationship yet. We live together & everything else couply, just not married. I see marriage as unnecessary pressure that has a tendency to put strain on the relationship. Right now if we’re happy together we stay, if we’re not we split. Simple. Marriage complicates it.
Estate can be managed by having a good will drawn up, and in NZ there is no distinction between a married couple and a defacto relationship (living together for >2 years) when it comes to separations and property.