Don’t think of it like this, because that is even more hurtful to you to think he just doesn’t care, never cared and you and your children meant/mean nothing to him. That’s not the case, he’s just a really scummy person who doesn’t deserve you.
I think the radio silence is more that he KNOWS he’s lost. He knows he has an amazingly strong wife who is far too strong, independent and with the support of a fantastic loving family around her will not be able to be swayed into taking him back, listening to his rubbish protestations of how it meant nothing etc. He has walked away because he knows you are too good for him, and not vulnerable enough (thanks so having this wonderful protective bubble of a close knit family around you) to be emotionally manipulated into putting up with his hideous behaviour because he can persuade you that it’s what’s best for the family.
In short, he’s been confronted by the visible reality of who you are, and who you have in your corner, knows he can’t complete and has admitted defeat. He’s lost, and he knows it.