I feel for you. Im a single parent to a SEN son who's now 12.5. I had to leave due to my ex being alcoholic, 4 years ago. I have had hopeless times, little support, couldn't use normal childcare due to son's behaviour, babysitters wouldn't come back. It did start to get easier around 9-10 years old, slowly my son started to be able to stay for a night with my parents and was able to tolerate babysitters. Now I have no issue with finding childcare for an evening, I am able to go out, I can sometimes even get away for a couple of nights.
I found a job working 90% from home which has been a life saver, I couldn't have worked otherwise. I managed to get a mortgage and now have my own house, I do live in a cheaper part of the UK though.
I even have had a part time relationship for the last couple of years, it has been hellish balancing even a few nights a month with partner with my childcare, but somehow it has been managed. My son is 13 in April and it feels that I can see the light at the end of the tunnel. He will be an adult in five years, I can do it.
You never know what is around the corner, I just focussed on one thing at a time and surviving each day.
I hope things get easier for you.
Do you know other SEN parents? It really helped me going for days out and activities with parents who wouldn't judge and who struggled with the same issues as me.