I think I would say something similar to ted27 that my advice here will be the same as it has been on the other threads, eg about life story work, about being involved in him engaging with birth family and supporting him, and you focusing on building your relationship and your connection with him now. It might be worth reading back on the advice on your old threads with fresh eyes?
I think a key thing here is him talking about his thoughts and feelings to you. I get the feeling that although he seemed happy when he was younger, he didn't talk frequently about his thoughts and feelings? That might have affected his feelings of not being connected? But if so it is not too late. For example, between the ages of 15 and 17 someone I knew was a really good listener, almost a sounding board, and this was really important, I was able work out my true thoughts and feelings, and how my own narrative differed from the narratives I had been given as a child about how I "should" feel. By being able to talk and work out how I really felt gave me confidence and helped me feel connected to that person. I was then able to work out how to build bridges over the differences between my own narrative and the narrative of my adoptive parents and the narrative of my bio family. The focus being on him talking now about his thoughts and feelings for as long as it takes might help build his confdence? I hope that makes sense.
One thing I have noticed is that when you start threads, your opening post is quite short, and each has a slightly different emphasis and it means the responses you have received have been quite disparate. I think it might be helpful for you to go back and do a chronological history - so saying how things were at each age, what he said at each age, what he said to explain why he wanted to call you about first names and how old he was at the time, when he stopped engaging in extra curricula activities, when he stopped engaging academically, when he has self harmed, what external help there has been and when,etc etc and do a more comprehensive opening post so that people have the full picture. If you just say "he has recently said..." then people may say that this is just teenage behaviour, whereas if you explain that he has always called you by first names, and that he stopped engaging in extracurricular activities a couple of years ago and stopped engaged in academic work because the teachers were so discouraging, then people will see it is more complex and that it goes back further than just teenage angst. This is just my opinion though, but I do think it would just mean that you would get more focused advice.
Incidentally I don't think that there is one set predetermined route for adopted teenagers. I know teenagers who went on to have adult relationships with both birth and adoptive parents, and I know those who went on to reject either or both of their birth and adoptivefamilies, and others who were rejected by one or other or both of their birth and adoptive families, and others who have swung back and forth over the years. You cannot assume any one thing will just happen. It comes down to the underlying relationships.
Re academics, when I was doing GCSEs and A levels I had recently moved areas and my new teachers spent most of their time on strike or being dismissive with most pupils at school (ie you have said you ds feels discouraged and I can relate to that) and for me it helped having someone basically saying ignore it, go in and do your best, just aim for good results in exams, and if you get through it you will move on to university and never need to see the teachers again. So my advice here is that encouragement and helping with strategies goes a long way once your ds has worked out what he really would like to do/study (I said that in your previous thread about academic work, though I had a different username in that thread - you wanted to help him and I said that that sounded great).
Just looking at your more recent posts Sw insisted she’s a good person, she tried and wasn’t always bad - despite the clear neglect in fact I agree with your SW here. There were reasons, as you have said, which led to the drinking, and there always are reasons - not excuses, but reasons. We all know how cognitively impaired we are with a relatively small amount of alcohol - by addiction stage the person has lost control. But my concern here would be that your ds understands alcholism as if he does go on to have a relationship with her, and she is still alcoholic, he will need to learn to cope with that, and to understand the affect all of this had on him at different stages of his life, so that he can make good choices for himself as to what he wants from the future. There’s no way he could have comprehended why she did all that though It is really tough to have a parent who is alcoholic but it is possible to learn to comprehend it.
Sorry that was so long.