Hello lovely op, I'm late to the thread ( I'm late to bloody everything! ) but have read it all and just wanted to add my support.
I too have a ds with autism who is doing his GCSE's and has quite bad anxiety.
I have some of the same issues as you, anxiety, depression, OCD and "traits of bpd" aswell as fibromyalgia and am currently being assessed for ADHD.
I've mentioned all of that to let you know that I really do understand these elements of your problems.
I can't even begin to imagine what fresh hell youre going through though over the other issue with "him" as I thankfully don't have any experience of that but I just feel like you need a big massive hug.
None of this is your fault. None of it.
He will pay a huge price for his actions and the best FUCK YOU you can give to him ( pardon fb language ) is to get better and start living. You deserve so much happiness, your son needs you more than you will ever know. My ds tells me often how much he needs me, despite being pretty Independent, he's such a mummy's boy but I like that 
I'm another one who is here to listen. I can't wait until Friday when ds has his last exam, they're making him so upset.
Weather is horrific here today in the north west, it has rained torrentially for over 24 hours and I find my mood always improves when it's nice and sunny.
Hope today is kind to you xxx