it feels whatever we do he throws it back in our face. We've really tried with him, tough love, calm talks, boundaries anything. I don't see how from just a short post posters are saying we don't/didnt parent him. And to posters saying he didn't become like this overnight - he did!
OP have you ever considered having him assessed for ADHD? The "overnight switch" is one way ADHD can present, as often with ADHD, the person is unaware that they are experiencing difficulties relative to others their age and they are resting heavily on strategies to compensate for these difficulties, often strategies like intelligence or quick-thinking, being very good at cramming or "winging it" at the last minute, being articulate/charming making people give them the benefit of the doubt, or giving a false impression that they have understood/remembered something they might not have grasped. This is not always obvious to outside observers such as parents, teachers etc.
The problem with compensatory strategies is that they are like a house of cards holding the whole thing up, and the demands on executive functioning (which is the name for the brain processes behind self-directed action towards a non-immediate goal, which are highly impaired in ADHD - this is everything relating to organisation, self-motivation, self-discipline, time management, impulse control, emotional regulation) increase sharply throughout secondary school and into young adulthood.
So when something stops working, which might happen because they have aged out of certain support (e.g. homework stops being as heavily supervised, projects are given as a whole thing rather than broken down into steps) or just the expectations of them increase because they are assumed to be able to manage (e.g. academic level increases past a level they can wing it, or they have more unsupervised time with friends) and because they still can't manage whatever thing it is they struggle with, but their compensation strategy to get them out of trouble is no longer working either, everything starts to fall apart and then the pressure of one thing failing leads to the next and it can look like a very sudden collapse, seemingly out of nowhere - particularly if something destructive like drugs is involved.
People will probably jump on me for suggesting it, but it is common and it is one possible factor which could be present and if it is present, it helps to know because there is medication and also strategies (and simply the understanding is something in itself).
I've seen the "sudden" turnaround in myself (went from straight A student assumed to be on track for university, to failing and then not bothering to go to class, getting a really unsuitable bf, dumping him but then rebounding with someone who seemed more sensible but was a car crash in other ways, teen pregnancy, single motherhood, almost drowned with the responsibility/overwhelm) and my eldest (went from doing OK at a prestigious school to just not turning up and scraping the bottom of the barrel with his grades, fingers crossed we caught this in time) and the opposite way with DS2 (went from angry chaos goblin who could not cope with school/school could not cope with him, to the point we were all querying whether he needed a special school, constant arguments at home, to a quirky but cheerful, cooperative and motivated child literally overnight on starting medication).