You poor thing. He sounds like very hard work.
Gas lighting you with number one! "... felt my husband upped the ante so to speak by making things harder for me- leaving a very needy child all to me to sort out- feed, sleep, handing him over and at one point leaving him crying in a sleepyhead (on the floor by my bed) because he was struggling to soothe the baby and I was in deep sleep so didn't wake up straight away," Horrible behaviour.
Telling you he has thought of leaving and sees you as a burden!
"My husband has responded by starting loud arguments when he's felt overwhelmed, accusing me of nagging him or shouting at him or overwhelming him when I've asked him to do something- eg. Take the rubbish out, etc. I feel nothing I say/do is right. I'm fed up of arguing with him- we can go round and round in circles for hours. If I refuse to engage with him, he'll keep at me until he gets a reaction..."
Yes, babies are hard work, so are older kids. Honestly, teenagers are bloody hard work too. But he is an adult, he needs to get help for whatever depression he has.
Because that's not nice or normal behaviour. He needs to get things sorted otherwise I think he may one day find himself on his own!
"Husband is currently having counselling. His last session is next week." I'd strongly recommend if he has come to the end of counselling and is still behaving like this then he does need more counselling.
I'd like to think things can get better for you both but it sounds like he has the problem, OP.
I am not sure if asking your health visitor is the best thing or not. I am afraid I might even be calling Women's Aid in your shoes because arguments that go round for hours when you have just given birth to your second baby sounds abusive to me.