Okay, the title is a little facetious, but hear me out because this is a hot take, or a psychotic rant... I'm not sure, but you aren't the same person you were 10 years ago, and you definitely aren't the same person 10 years before that. I mean, think about how much you changed in the past 5 and tell me honestly you won't change 5 more years down the road. And the thing is no one stays the same. Not you, not your friends, and definitely not your sweetheart.
So people say to wait forevermore for marriage because you just don't know someone unless you know them for like 5 years. That's nonsense. You still won't know who they will become. It seems to me like the majority of people expect the wrong things from a marriage, like an ideal person to always make them happy and be whatever they want at the time rather than a partner to help and be helped by as you work towards a common goal that's bigger than yourselves. The key to a long lasting marriage is to not get divorced.
Now, I often hear marriage as a business agreement when things like this get brought up. It's not. There's a spiritual side to marriage, like a mixing of souls kind of thing. If you aren't the spiritual type, you can think of it as spending so much time with someone, your personalities mix with each other (also a danger in long-term relationships). It's fine for marriage. It's supposed to be like that, but I also believe that break up of long-term relationships or marriages damages a person's soul, like they became a part of you and when you reject it, you reject a part of yourself. The trouble is that personalities change, so basing a relationship on personality only is unstable. It's just as unstable as looks, which also change (yes, my title is a clickbait lie).
So base marriage or long-term relationships on something bigger than yourselves you decide to stay committed to all your life. Decide to just make it work, and then follow through. It's really the only thing that makes any sense.