@ Hopefullynothingtoworryabout
I'm so sorry you're having such a crappy and worrying time with your DC and the stresses of late pregnancy and Covid 19 added on must be absolutely horrendous. 
I'd suggest, when you talk to him after DC is in bed, simply saying to your DH 'I need you to listen to me and not interrupt, OK?'
Then say something like ' I know we agreed that I would be the primary care giver for our children, and I still intend to do so, but at NO TIME did I agree to be the SOLE care giver and parent. '
'Your emotional and physical contribution has been non existent for a long time, and you even outright lie to me to avoid spending time with us. Until now, this has been brushed under the carpet in the busyness of normal day to day living, but it either ends now, or we actually begin to talk separation but you will have to change either way.........I cannot continue to be the only parent our child has as the added stress of our DC's medical needs, the imminent birth of our second DC and the risk of Covid 19 has altered my life, and the total LACK of understanding, concern, love, care, thoughtfulness etc has become insurmountable for me.'
'You have two choices, either you tell me things will not change for you and you will continue to not give two fucks about me or the children................or you tell me exactly HOW and WHEN and WHY you WILL change things and give your family the love and support we need, because love and support are NOT money.'
Either way, your life is about to change forever, it's either going to be WITH your wife and children, or as a divorced man with support payments and child visiting days, for which you will have to parent ALONE, as I have always done..........You can let me know your decision tomorrow morning, goodnight.'
I wish you the very best, both for your DC's health, the birth, and for the future of your family. 