There are no hard rules that apply to everybody. I would never marry someone without living with them first. I have personally found that once we were spending a ton of time at each other’s houses, to the point of doing laundry together and planning groceries etc together, then it just made more economic sense to stop paying for two homes when we were spending all of our time together in one or the other. Some couples never get to that point, though - some people like their space, or like to just keep certain things separate, or just don’t want to get married, and that’s all awesome, I just can’t really speak to that at all, since it’s not my experience or style.
My husband and I got our first place together after dating for 8 months, but we had been basically inseparable for most of those 8 months, and we both had local family and friends we could fall back on if things didn’t work out. If I hadn’t had a social network to rely on, or if we hadn’t spent pretty much all of our time outside work and school together (so we had seen each other stressed, hangry, sick, etc), I probably would have been a little more hesitant to make the leap that quickly.
We started dating June 2004, were married January 2007 - we joke at every anniversary that it’s “16 Blissful Years!” or whatever number 😂 and they’ve mostly been great, but life is hard and relationships are hard, nothing is bliss always and forever. You find a best buddy that you think is super hot, and you make little moments of bliss together, imho that’s all you can do. ❤️
And even relationships that don’t last forever aren’t failures - even if you move in with someone and you break up, you still learned and grew from that experience, and that growth will make you a better person, and maybe the next time you’ll find a better match.