Young People Living Together

So, now all of my children are adults, and I am living the empty nest life, however....I DO have grandchildren. My oldest granddaughter is now 20 years old,( and yes,) she is the same age as my youngest daughter, and I know that sounds strange but that's how it is! My darling granddaughter has just moved out of her family home and into the home of a boyfriend and his parents. I guess there are more grown children living at home that there used to be in my day of growing up. She has done pretty well for herself though because she is a licensed cosmetologist and is still in college for business classes, she works and that's her life right now. I was very uneasy about her moving out, and of course being my first and oldest grandchild worried about her moving in with her boyfriend. I think that I worry about her just as much as if she were one of my own children. When is it the right time to move in with a boyfriend? Is it better than just getting married first? How do they take care of finances and how do they split living expenses?  I am just curious, as they are young. I guess they must look at it as if they want to split up at any point, they are free and do not have to go through the paper work as if married people do. This seems to be the normal thing these days. How do you feel about it?