Holly, I'm so sorry it is tough for you especially when you have such young children but they will give you joy in a few years.All the hard work will be worth it.
I think you are at the stage of awakening, trying to fit the pieces together whilst also struggling to get through the day.
I felt completely drained by ex and didn't realise the extent until I left.I now have the same workload, probadly more as ex did household chores but I feel much better.
I also get more support as obviously a single mum when in reality I was always single but married.
A line in the sand for me was "would ex be there for me if I was ill"..I knew the answer was No as he had proved it many times.
Ironically I have been ill post separation and have felt so supported because I now surround myself with those who genuinely care for me.
I suspect you are a very strong person, which is why you are focussing on chores.However I think your needs/feelings have been invalidated for so long that you have lost touch with what you need.
All I can suggest is prioritise yourself, if money allows, then outsource what you can.Get yourself into a strong financial position, savings in your name and make sure you are knowledgeable about all finances.
If you separate it is in some ways easier as the children grow up not knowing a difference and they are accepting.We all want the united family but it doesn't mean you and the dc can't be happy.
Do start to tell close family or friends