itdid Camhs and SS when we had problems, god it is a long long story, but I am concerned that what I am seeing now is unhealthy at times and beyond norm teen behaviour.
I am shattered. I have supported the healing of DS and his Dad's relationship and worked hard with them both. DS is torn between hating him and never wanting to see him and then asking to go for extra time with him and them being very close. He will walk out of his Dad's after a row and they both have a tendency to say whatever vile stuff comes into their heads at the point of anger, and twisting everything you say to suit them. But Ex id an adult and DS is 13, which I am finding scary because he is very much a young person, but approaching an age where indeed his actions will be carried through to other relationships 
Itsnearly, you are absolutely spot on, The poor kid went through stuff that doesn't really make it a great surprise that he has difficulties. I am struggling between doing long detailed posts that would make it clear why we are in this place and not 'drip feeding'.
Basically, his Dad, from whom I am separated has a difficult relationship with drink and anger management issues, and possibly an undiagnosed personality disorder.
I suffer from Depression which, hand on heart I have worked through counselling and personal development to control it and rebuild my self esteem and deal with my own past issues and overall, improve the home life for my DC's (I also have DD8).
He is so like his Dad, and it hurts because I do think he needs help but CAMHS and SS wouldn't entertain taking him back on.
School sees a bit of what I get.
He is funny, charming, we have lots of hugs, laugh a lot and tease and banter. He will come and sit with me when I am in bed and just talk.
When we are like that, I can reach him, he recognises how he is and we talk positively about how we can work together to sort it. And I am open to him saying OK but you know Mum, it annoys me when you do X or Y....
And then the next day we might have just as well talked about the weather. He can be beyond cruel to his sister, who has started to retaliate, but it is like a switch is flipped and I can't reach him. Just like his Dad. Funny, intelligent,capable of being so kind and tender, talks and seems to listen and you think 'hey' we might actually be getting somewhere' and bam 
I look in their eyes at that point and it is like being with a stranger.
But stick them in a office with any of the specialists we have seen and the charm and general picture is of two people that don't really need help and that I am perhaps fabricating and exaggerating as a result of my depression. And please believe me, I am not.
My own problem right now, which I do have to deal with is that I am fed up of fighting to get any help, from putting socks in the wash basket, to getting the washing up done once in a blue moon, being moaned at every meal that I cook because, 'it's tuesday I don't like mash, I only eat one kind of ham'.. I don't pander to it and they just get what is on the menu... but it is exhausting... the usual pile of plates in his room, turning up later than arranged,... contradicting virtually every decision that I make as a matter of course..
I give him a £1, he wants 2,
I ask him to be in at 8.30 he says 9,
he's hardly got anything because it is all broken, he will smash things on the drive just because, well, he doesn't know, i.e a phone charger belonging to a phone that just needed unlocking, he swung around his head and smashed on the wall, and left the bits all over the place.
I am calm, generally, try not to raise my voice, (DD is frightened of shouting) assertive, don't engage, try to be flexible if he wants to discuss something reasonably, but it builds up and I actually want to shout and rant and say all the things that come into your head because quite frankly I am fed up of being a lone parent and how much bloody hard work it is.
But I am the 'safe' parent that they both admit to needing. And I want time out now.
I want to say, 'hey, I am going to a friends tonight and share it with him without then having to worry if I will have my evening sabotaged by a stream of emotional texts. And being torn into confusion by guilt and worry and just thinking FFS can I not just have a night off? And the other option of having to do it secretly which just is just so crap.
This morning, I found pieces of fruit all over the drive and on asking, initially why, discovered from DD, that DS and his mate had taken a kitchen knife and some fruit and were throwing it in the air and trying to slice it as it fell. Not best impressed but sort of but DS was angry at DD, said he knew nothing about it, I said hey, it's not that big a deal, just be honest with me OK, but he was too far gone. He pokes and pokes and with the best will in the world at some point
And it all starts coming out, it is as if he sees himself as my parent, and says that I should be punished when I mess up. as we are trying to get ready for school, as he refused to leave the house and I had got annoyed, I stated that he had to go to school and I wouldn't give him a cheque for a school trip unless we could leave the house so he could catch the bus. I gesticulate with my hands a lot and as we stood by the door, he reached over grabbed my hand and squeezed my fingers.
I shouldn't have said anything about the bloody banana but it was just one of those moments, I never envisaged it escalating.
I have to work, I am sorry for offloading and ranting, and thanks......
We've come a long way but still have a long way to go it seems