This is my first posting on this site.  I have been reading the forums for years and have found them helpful.  I am looking for anyone who has had experience with disengaging from a misbehaving teenage skid and what happened when they turned 18.

There is so much to tell, but I'll try to keep is brief.  I've been with my fiancé for 4 years and he has three kids, all of which I've always had a good relationship with.  DH and BM separated almost 7 years ago and are divorced.  We now only have SS-15 left in the house and we share time 50/50 with BM.  When older brother left for college, the freedom and lack of supervision has resulted in some very bad behavior that continues to get worse and worse.  SS is currently on his way to failing out of HS, he smokes weed regularly and lies.  For the past year and a half, the only thing my fiancé and I have real arguments about is SS and how to turn him around.  The main issue has been a lack of rules and consequences, but at the end of the day, I am not his mom and I cannot enforce anything. 

Recently, things got really bad with SS lying, we found drugs in his room and his grades continued to get worse.  Somehow he hasn't been kicked out of school yet, but I feel like it's coming.  After the s**t hit the fan about 4 months ago, DH and BM got SS into therapy since he said he was so angry because of anxiety.  Also, a few weeks ago he started going to tutoring twice a week to help with his grades.  Unfortunately, there were other clear rules and consequences that were laid out for SS, but those are not really getting enforced.  With therapy and tutoring, DH and BM feel like things will magically get better and all aspects of his behavior will improve.  They are not.  I was involved in the "family sit down" with both parents and SS and I thought we were all on the same page.  Unfortunately, the "rules and consequences" put in place are not being enforced and when I ask DH about things that happen, he tells me that he gets the final say and doesn't want me to second-guess all of his decisions.  This is hard since we have always communicated well, but when it comes to this child, I really don't get a say and it has been causing a major strain my my relationship with DH.  A few weeks ago I hit my limit and decided to start disengaging (meaning, I don't want to know about grades or about SS lying, I don't care where he is, what assignments are missing, etc).  When I know too much, it just makes me angry that no one else seems to want to do anything about it and my "reminding" DH of the agreed upon consequences only causes conflict.    

I have only just started stepping away, but I feel good about it.  I care about SS, but it is clear that my "help" and opinions don't matter right now.  I am willing to step aside and let the "parents" parent, but what will happen when SS turns 18? 

Disengaging sounds like a great idea, hypothetically.  I have read plenty of stories that give me hope for my sanity.  However, my concern is what happens when SS turns 18 and is now technically an adult.  I have made it clear to DH that I do not agree with the behavior that is happening now and that I will NOT agree with it when he is 18.  If he fails out of HS or moves on to harder drugs, he will not be able to work toward being an independent adult.  I know we’re 2 years away, but I'd be naive to think all of a sudden "our house rules" will suddenly be enforced.  Although he will likely move in with his mom since according to him he "hates living in our house", I wonder what happens when she gets a new boyfriend who refuses to put up with his crap and says he can't live there. 

Have any of you had a personal experience with something like this?