One of the luckiest accidents of my life was British visa restrictions forcing me & my girlfriend to decide if we were truly in love or just pretending.
Marriage is an utterly insane mechanism. You’re right to think, “I’m not sure, what if it doesn’t work out, I lose so many options, etc.” It’s a crazy, impossible-to-guarantee decision with huge downsides. But if you do it right, the upside arguably approaches infinity. People postpone marriage for the same reason they're becoming less religious: we've lost the capacity for faith.