Going out for a nights out after my first was born telling me he would be back in a few hours, staying out for days and ignoring my texts asking if he was ok. I was in bits thinking the worst and he would roll in days later or calling me demanding I pick him up at 3am because he was injured/in a bad way
So most likely he's been cheating on you for years, this would be what he's doing while he's been gone for days.
But, more importantly, he's physically abusing you. He's holding you against the wall by your neck. This is very serious.
Please, please, please call 101. Please. If not for you, for your children. Imagine them being held up against a wall by their neck by this man.
Did you have an abusive childhood (or are you not aware you did)?
I ask because I had one, and the behaviour you describe I saw a lot of. My family also used to tell me that everybody screams and shouts behind closed doors, in 30 now and still find it hard to believe that that's actually true.
It's damaged me mentally beyond description here. But I suffer everyday due to behaviours I witnessed as a child and my mother or grandmother being held up against the wall by their necks. Sometimes it can come out in anger myself. But, like you describe, there were days when everyone was all sweetness and light. It doesn't mean the abuse isn't happening though.
I tell you this because as a mother, surely you don't want your children to suffer in the future? If you don't, then you know you have to do something and quick. You need this man out of your house, and quick. Call 101, call women's aid, please be proactive for those children. Really, you have to do it, you just do.