I've been here too. I am so sorry.
If I have any advice it would be to cut him out now...out of the house, out of your thoughts and out of your future. You will go around and around in circles worrying about him, what he thinks, what he wants, what he will do next etc etc. Just stop. Use those thoughts for yourself and your kids. Focus everything into that.
Historically he has not pulled his weight for the whole of the relationship....you have to get up at 4:30 am? How? It is a wonder you haven't had a breakdown yourself! If he decides he has changed his mind and wants to be part of the family and with you then what will your life be? Panicking that he isn't happy but hiding it, running about all day dealing with house, three kids and a job while he does what exactly? Never feeling good enough, never feeling like you have worked hard enough. Don't do it!
Mentally let him go....it is painful but you need that energy for yourself.
This is what worked for me:
Do day by day. What do you need to deal with today? Do that. Sleep when you can. Practice deep breathing. Get professional help...doctors, health visitor, citizens advice. Make a list so when you brain is everywhere and you can't think you can look at the list. Make sure you practice self care and acts of kindness to yourself. It will build you up and help with your self worth. Don't believe his criticism of you...it is only a justification for his actions and nobody deserves what he has done.
Some days it will be all too overwhelming....just get through the day and start again the next day.
When 'he' would creep into my thoughts I would close it down best I could..distraction etc. Things can trigger you to remember good times or think of what could have been. These used to floor me making me useless to do anything else and totally upset. I learnt to cut it off so I could function.
Your post sent shivers down my spine. I was you five years ago but without the newborn. It was so traumatic. I promise you that you come out of the pain and just have a revelation that this wasn't you and that this wasn't your fault. I also think another woman will pop up out of the woodwork. It is so common in these instances.
Whatever his reasons are or whatever he has going on it's not about him anymore. Sadly, you cannot trust him to be on your family's side anymore.
If you are on instagram there is a lovely community called 'frolo'. Many people in your situation sharing issues and supporting each other. Maybe look at that? Any source of help is a source of help. I have also linked through from there to other accounts of other single parents who are sharing their stories. Stuff like this made me feel less alone. In my family and friendship circle, unusually, there are no single parent families/co-parenting families.
For you it's about you and your kids if you keep,focusing on that you will get there.