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.
Just get married in law. You don’t have to go through the whole wedding thing if you don’t want to.
It depends where you live and what local laws are but usually it’s called something like “civil partnership”, it’s legally the same thing as a marriage and grants your partner all the same rights as they would if you were married.