DSS16 living like a hermit and DH seems to be in denial

Thanks for answering my questions OP, so it seems that you've been in your Step Son's life since he was 6, in which case I do find it quite surprising that you don't feel able to approach him about what's going on. As you've said that he does come in to have dinner with you, I think it would make sense to use this time to ask the questions posted by 'Rocknrolllife' above, as they are all what you call 'open' questions, whereas the chances are, that unless you're in sales, you might be asking questions that can be answered with yes or no answers, which really close down a conversation.

You say that he might be with you for a full 48 hours, but you perhaps only see him for 10 minutes in the whole of that time, so if your DH isn't stepping up to help his Son, then in your shoes I would be. I would be making a point of going into the room where he locks himself away, and asking him to come and join you in the house, even if he only wants to do gaming, as at least that way he will know that you actually want him there. Maybe the fact that his Dad is too busy doing DIY, makes him feel like he's unwanted, and in reality, most lads of his age from a broken family, wouldn't be bothering to go and spend much time with their Dad if they felt like he didn't want them around. Ask him to tell you about the games he likes to play, what it is he likes about them, maybe even ask him to show you how to play, if you think it would help. Have you ever suggested that he might like to bring a friend over with him for the weekend?

It seems to me that you really either need to take on some responsibility for this lad yourself, or have a very firm conversation with your DH, about teenage boys and suicide. If you're not aware of the statistics of this, then I would suggest that you Google 'Teenage boy suicide rates UK', it really is a huge problem, and neither you or his Father would be able to forgive yourselves if this young person was to take his own life. It seems that his own Mother is so wrapped up in her own life, that she's not taking notice of what's happening with her son, and as human beings, I think we all have a duty to help anyone who we think is struggling.

he should definitely be more comfortable with you. Do you go on weekends away, days out, visiting family/ friends or a summer holiday?
how is he away from his computer will he socialise with you then?

That sounds awful. The problem is if left, it is quite likely to continue for years and that will be her reality. I know it's not your problem, but perhaps you could ask for the daughter to help with a problem - gardening, housework or some help with tech? Seeing and knowing what's happening right across from you must prey on your mind.

The neighbour approached me and asked me if we would old her daughter to babysit for us, I think it was her way of trying to help her. She wanted us to pay her a fortune an hour though and we already have family that babysit for us so we didn’t take her up on the offer. It would be difficult to approach the girl with another idea like gardening etc because I would need to go through her mother and she would control the whole thing. Yes it’s definitely difficult to watch

Oh what a shame the mother said that. Perhaps speak to her again and explain that it currently doesn't cost you. If she had felt that offering money would be the only way to incentivise her daughter, maybe she could "privately" pay her daughter to babysit for you, so that her daughter wouldn't know that she was paying. All very difficult.

He has MH problems, as evidenced by the fact that he cannot function normally.

He needs an intervention.

What "parenting"? He's having a laugh.

It sounds like it's reached the stage with your husband that you need to scream and shout and stamp your feet if necessary OP, as his son needs help, and he needs it NOW!! In your shoes I would be tempted to say to him 'I don't care if you think I'm being patronising, and yes, I am criticising your parenting, as you're not actually doing any, and your son is suffering because of it!' Are you scared of what he'll do if you really kick off about this OP?

Personally, if he's not prepared to step up, and you can't get through to the lad, I think I would find myself needing to walk away, as it seems that your DH really doesn't care, and I couldn't live with someone like that, but obviously the choice is yours.

I was just like your stepson I had an horrendous time at school I was bullied from the day I started to the day I left
just wanted to keep myself to myself my bedroom was my sanctuary felt happiest in there just on my own

when you go out and see everyone with friends and doing things it’s sole destroying and if you will rubs your nose in it
every now and again my mum would get on at me about going out and meeting friends to the point I’d just lie and go out and wonder round for a few hours in my own to get her off my back
THERE IS NO SILVER BULLET to get him friends and a social life

i came into my own when I started work and joined a gym got a social life and a friendship circle never looked back