Most Helpful Guy
Most 19 year olds of either gender have NO experience living on their own and being responsible for EVERYTHING about themselves. And the more they were coddled and "taken care of" by their parents, the worse they are going to be when on their own the first time. And in fact, the stress of being on their own can make people even worse then they normally are.
That's what you are likely getting into when you move in with ANYONE at that age: a roommate that is either messy, doesn't respect your stuff or boundaries, can't manage to pay the bills, keeps you up all night, or whatever. You'll learn that a lot of people don't live like you do, or have the same values and morals that you do, and they'll be difficult to live with.
Most people get better with time and experience (and others need to live on their own forever), but at 19, most people just don't handle it well, and normally the "most responsible" person ends up having to clean up the mess and gets stuck with the problems and bills.
Then, if you add the additional problems of a romantic relationship on top of that, you have a recipe for chaos and potential life-changing issues, such as pregnancy.
I recommend that if you're going to move in with someone, move in with them, and keep your name off of all of the bills and lease, so that if things don't work out, you can move out and not have your credit and ability to rent screwed up for years. Obviously, you should be responsible for yourself and not screw your roommate out of bill money or whatever, but you don't want to get stuck in a situation you can't get out of either.