My first thought is also that you're Autistic. It's highly heritable. I see posts continually where women especially have been diagnosed with multiple MH conditions and they're actually Autistic - and possibly those other conditions aren't accurate.
I feel it is actually normal for many people to feel suicidal. When you consider that you have the stress of raising a child with additional needs in the way you describe, then consider you've probably been masking your whole life and are trying to operate in an NT world that's unforgiving. And whatever other stressors, well it's understandable right now that you feel hopeless.
Medication - the GP can prescribe anti depressants to try. You can tell the GP you have a very strong sense you're Autistic and can you be referred for assessment. You don't ask their opinion, you tell them you believe this to be possible and can they help with referral. It does require being firm which I know is tough when you're so vulnerable.
Samaritans - they are great to cry to when in despair. They don't try talk people out of suicide or panic at the mention. I think this is so important because you can just be honest without fear of panic or ingenuine responses through fear reaction.
A break from your child - some respite from parenting would help you alot. You need a break. I have a teen who is Autistic, ADHD, lots of challenges in different ways. It's too much with no respite. Social services might help if you're saying this life is making you suicidal. I believe there's not a risk you're losing your child if you appeal for help. The challenge is resources.
Can anyone care for your child to give you regular breaks. Benefits like DLA for the child might help pay for support ( if you don't already have it).
A therapist who is familiar with and understands Autism would be a much better fit than anything like CBT for you. I have my own, who I found years ago. I pay. The NHS is appalling and sub standard in what you might get.
When you're on your knees, doing all this is so hard and you might have no will to even try.
If anyone in your life can help you sort some of these things, reach out to them.
You have nothing to feel ashamed or guilty about. Many mum's want help and are desperate to escape and feeling suicidal is not your fault but a response to utter despair this sounds like ❤️
If you have bipolar, the medication for that is quite particular I understand. Seeing a professional who understands autism might help you learn if bipolar is also going on or if actually that's not where going on here. The two can co exist.
Loads of hugs to you.