I've dealt with this exact situation many many years ago, and I ended up taking it in the shorts over it. Rent, phone expenses, food, utilities and the like. I sued the other person in small claims court, and it ended up being pointless, as they left the state and pretty much disappeared. Cost me $1500 or the like, after I figured everything into it. They eventually left right before I kicked them out, so it ended up being a moot point, though they still stuck me over the costs.
You either have to put down some clear rules and clear lines of what's what, or you have someone that will walk over you in your generosity. If nothing's in their name, there's no penalty of their money not being applied to the bills, it's all on you and your credit rating.
The landlord will only go after you for missing parts of rent/utilities/whatever, not the moocher. If their name's not on the lease, they have no legal right to be there, as it ends up being a your word against theirs situation.
As senorwoohoo stated, he was in a very similar situation, and he eventually left the situation with his asshole roommate. Ended up being better in most ways, and not better in some ways.
You're working towards a really bad situation, again over being kind and generous to someone else. No one is saying you shouldn't be kind or generous, though in a situation where someone is taking advantage of you, you need to look out for yourself, as the moocher such as hell won't.
One place I recommend to find out your legal rights is the Nolo Press website, where they make more than a few books about renter's right, tenant law and landlord law. Website for renter's rights is right here:
http://www.nolopress.com/resource.cfm/catID/31250834-6A2E-4970-9EDD4DAF221A0C7E/104/138/
I suggest you take a look at and see what your options might be.