Lynne,
(cece took my bad apple line) but I'll say it again, don't let one bad apple decide what is real in your life.
I tell myself that I wasn't the best mom while my kids were growing up, but you know what? I did the best I could with what I had at the time.
Time goes on, as some people say it's time for him to poop or get off the pot. At 18, he's probably still somewhat immature, but you deserve respect from your child, as all of us parents do.
I say, stand up for yourself, stop the guilt you have right now, this very minute, and tell him he either contributes to the household and treats you with respect, or he's out on his ear.
Don't buy into what others think, heaven knows they haven't walked in OUR shoes....
Hugs yo you,