I'm so sorry its terrible what has happened, Men are a joke he just swans off expecting you to take care of 4 boys by yourself! think the 1st thing you need to do is get to court to make sure that you are protected, the sooner things are in the courts hands the better, as I've seen guys selling their houses out from under their wives feet, putting assets into someone elses name all to make sure the wife doesnt get anything if you speak to a solicitor they can make sure he doesnt do any of those things. If he has anything to his name,
If he isnt prepared to properly support you I'd also be going to court to make sure he has the boys certain times during the day so you can go out and work if he has to sort out childcare when that is so be it. Just dont sit back and be walked over. Also are their any state benefits you can claim (I'm in the UK) if you have access to any joint accouts clear them out before he does and if you have any accounts he has access to close them and make sure you press charges if he takes any money, change all your money passwords and secure your future.
I know this is a difficult time for you but I have been in a similar position luckily living in the UK we have a benifit system which makes sure you never go without, food, shelter, and medical care.