PeggyP,
I sympathize with what you're going through. My 18 year old son is definitely trying our patience, too. Although mine has graduated from high school, he's not doing very well in college, and we have discussed "what next." We have seen a family counselor, and that has eased some of the tension between my husband and me, even if our son continues to demonstrate poor judgement. We take it one day at a time.

Was your son always "a handful?" If not, then like you, I'd probably question if his attitude changes were due to substance use of some kind....Since the drug testing came back negative, I wonder if he's ever been evaluated by a mental health professional, because there are some conditions that become more noticeable in later adolescence...I know at 18 you can't force him to see a doctor, but it sure seems like something is going on, especially when you say he can't keep a steady job, etc. Does your son talk about wanting to move out/drop out of school, or is it just your husband who wants him to go elsewhere?

Like sbozarth suggested, I really think it would help if you could see a family counselor. Truthfully, it would be ideal if you could set something up with a person who could be "evaluating" your son for possible mental health issues even as your family sits together in the session, since I doubt your son would agree to go for a private evaluation himself. He probably doesn't think anything is wrong with his behavior, everyone else is the problem.....Here's an article about compulsive lying and what else it might signal: www.mental-health-matters.com/articles/article.php?artID=153