Trouble at work and being reduced to nothing

I've had my job for 16 years.  I'm 51 now and a couple of years ago I realized there was more going on that depression (which I'm treated for) and discovered ASD may be at work too.  I'm untested, and my Doctors practice in London is overworked and couldn't give a *** (everyone a bit autistic, deal with it kind of vibe). I've had severe meltdowns which led to suicide before, but I've always been able to work, sometimes even better and more focused, and my boss know this. Last Year I decided to be upfront with him about suspected ASD which I realise now was a huge mistake.  I was on a management course, which I enjoyed.  Once completed, he sent me some CVs and said he was now recruiting a manager externally.  he's also encourage me to have an assistant to cover my days off, who now know more about what's going on in the department than I do.  He can take the assistant to the pub and have lunches and to work events, which is something I was never good at, and seem to be his priorities. He puts the assistant on projects I don't know about, and introduces him to senior management when I'm not around.  

My work has been consistent, and I like my assistant a lot and we had a good working relationship. but at the moment it's pretty obvious that my boss thinks I'm too made to too a job I've worked for 16 years, and want someone like himself to run the department.  I suggested I could take a role on the training team as I'm a good training and enjoy getting my hands dirty. He suggested I take a back seat and do junior work while my assistant does my job.  That's how much I matter.  

I feel like I need to work.  I need the structure and I'm good at it. I've trained many people, including my assistant, other supervisors, and I'm sure I'll have t train the new manager too.  I trusted my boss as he know I had issues and I never let him down.  I feel like he's taken the opportunity to exclude me from everything on he ground that I'm "a bit crazy", and don't drink enough.  I've been told to not to recruit people my age too.  I'm being shut out and it's starting to trigger me. I left the office after 30 minutes on Friday as I needed to run.  Just run and get away. But I have no where to go. No friends, no family, nothing. When I feel like this I don't understand what I'm doing here. I've got at least 25 years left on this planet to be treated like *** over and over again. But I have to be good and go on about how lucky I am and "enjoy everything" and be a good pretend person, so people can take advantage of me even though I'm trying so hard.  It just feel so hard when it's clear I'm not wanted here. I hate it here.  I'm trying so hard and it's never enough.  I feel like I'm just alive to spite everyone.  But no one gives a ***. It this what I'm supposed to do? It feels really ******* hard right now. I though telling people would help, I though identifying myself would help.  I have never felt more worthless. Sorry for triggering people, but it's times like this when I just wish I wasn't here. I don' want to hurt myself, I just don't want to be here.  I've been here so long already and I'm so tired.