I empathise. I was on my own with a 1 and 3 year old. Elder DS is autistic and very challenging, one of the many things XH couldn't cope with.
I had to do everything. At a particularly low point i remember stroking DS2's back as he threw up in the toilet, having spent the night up with DS1 doing the same and saying 'hurry up mummy needs a turn'.
8 months is quite a challenging age. You don't get very much emotion back in return for all your efforts.
Everything is worse when you're exhausted too. Sounds like you are.
I had a lovely supportive friend who felt we were in the same position because her husband, on £70k, worked away most weeks whilst her parents took her DC whilst she worked.
When DS1 started school I missed so much work because nursery and school couldn't cope with his behaviour/ he couldn't cope with school I ended up giving up my business.
Life has turned a corner. The divorce came through, we got beyond court. I managed to sell the house. It took me a couple of years but I found myself and worked out what I wanted. The DC got older, easier and more responsive. I learned to accept support when it was offered.
Then I started dating again had a wirlwind romance with now DH and remarried. Not that I'm saying a relationship is in anyway a key.
On bad days it feels like life is over but really its just a new chapter and life is beginning. You sound like you're putting everything in place with studying and volunteering to work out what you want and be fully in control of your life.
Hopefully if your DD's been up all night you'll get the chance for some rest today.