Sorry to hear that. My ex did something similar. We had an argument one day, he walked out and never came back, didn’t say a word to the kids. He’d been having an affair and planning it for months ( I’m not in any way suggesting that this is the same for you).
It’s so difficult and you probably don’t know how you’ll get through it but you will and it definitely does get easier. Put all of your effort into being the best mum you can and take one day at a time.