The point of life story work isn’t that they know the facts, it’s that they understand and are able to process the information about their early years, can process the trauma that inevitably comes up as they understand what their own life story means to them. The sw was utterly wrong in saying he didn’t need it, but even if he did have that work done then, you’d be revisiting it now because his cognitive processes are very different now and the support he needs is different.
I’m guessing you’re in Scotland given you talk about 5th year, post adoption support is accessed differently here than in England, where many replies will be coming from. We don’t have “post adoption support” in the same ring fenced funding way, it’s accessed through your local authority adoption team. The reality is that most therapeutic work is contracted out and in many areas Barnardos are contracted suppliers for life story work - they provide an excellent service and have a lot of research and specialism in this area so I’d take them up on that offer.
If you think your son will contact (or might already be in contact with) his birth family I’d ask the local authority to arrange support for this, it’ll likely be someone like The Red Cross or Salvation Army that actually provide the service but the LA would pay for it.
In terms of attachment, I’d ask for a referral to CAMHS, it’ll take ages - and depending on age he might be close to aging out - but many CAMHS services have a team specifically for care experienced and adopted children, something like DDP may be really helpful or therapeutic life story work which sometimes falls into CAMHS remit. If CAMHS either won’t take him or he’s at risk of aging out, the local authority may be prepared to pay for a private practitioner so really press them on it.
You’re going to need to be tenacious, getting support for teenagers who aren’t presenting “clinically” eg self harm, depressed etc is difficult, and some presentations in teenagers get addressed as behavioural instead of identifying therapeutic need. His care experienced status helps here because it creates a duty on the local authority to support him beyond 16, which is their usual cut off for children’s services. It’s also work looking at COPEs website, while their service is for families where a child has additional support needs your son falls into that bracket by virtue of being care experienced - in Scotland children who have been in care at any point are deemed to have additional support needs unless they are specifically assessed not to have, which is useful in negotiating with schools and support services.
It’s going to be challenging, and I know how distressing it must be for you to hear he doesn’t feel any attachment to you. Do hold in mind that this struggle with his identity is part of his developmental process, he’d be questioning this stuff regardless of how he’s been parented - adoption just adds another layer to a pretty shitty cake. It’s so common for teens to have a romanticised version of their birth family - it helps to protect them psychologically against the impact of knowing how really awful their early years were, good therapeutic life story work will help him pick through this and deal with the emotional fall out. It feels like a huge rejection, but he’s really trying to keep himself safe from the impact of his past and his fear (unfounded and sub conscious) that you’ll leave him when he’s old enough or when you get tired of him. Telling him is good, but this isn’t a logical, cognitive process so you won’t be able to reason him out of it but the reassurance is important.
Also maybe look at counselling for yourself, to help hold you steady while you hold him steady?