Do Rules Apply?

When you're "roommates" with your grown adult child, are there rules that apply?

My son is 34 and recently moved back home.  He doesn't seem to have his life on track, owes money to many different credit cards, and as nicely as I've offered to help in this arena, he hasn't done anything with it that I can see.  It's not really my business except for the fact that he lives in my house, I am charging him only $400 in rent, and that includes food.  (hell, he eats that much in a month!)

But sometime Sunday it seems he left the house, and didn't come home to sleep before work - he works the night shift.  While I made him lunch, his bedroom door was closed and I thought he was asleep.  His alarm went off and he didn't get up, so I knocked on his door.  Nope, not in there.  So I turned off all his "stuff" and closed the door. 

But here's my question:  if you're roommates, what are the house rules???

If you're going to be gone, should you leave a note?  text msg?
If someone is helping you out of a jam, should you help around the house?

I realize that as a mom, I can't expect him to live by rules that I established when he was a teenager and still under my roof.  But at the same time, it's my house and I need to be comfortable with things.  Last weekend, he had a girl over just before midnight.  It bothered Sadie, and she woke me up several times. I finally had to tell him that his friend needed to leave.  It IS my house, and since I'm footing the bills, I need to get my sleep so that I can go to work.

I felt bad about that situation, but what about the house rules???

My biggest fear is that this girl is really just a girl -- and I suspect its the daughter of the woman he was living with for two+ years.  Which in my opinion makes her too young for him.   I'm at a loss as to where or what to do next. 

Other than create a set of house rules, and make them stick.
It sucks trying to do "tough love" on your grown children ....
but sometimes it's necessary.