Op this must be a big shock for you both emotionally and financially
Do you work? If so you need to look into claiming tax credits and working tax credits
Your ex will need to pay 25% of his net income to you as maintenance
You would be encouraged to sort out residency of the children between you so that both parents play an active role in the dc lives. Lots of shared care is done as every other weekend, shared care during school holidays and shared bank holidays etc.
Oh and make sure you put in for tax credits and child care tax credits now, apply for the firm's today and get the ball rolling - then you will know how much you are entitled.
Put in to your district for ,25% reduction for lone adult in household.
Once you have then established your income you will know whether you can afford to stay move etc.
This is all the practice stuff
But emotional feels will come into play with both of you.
Men rarely leave without having someone else involved, you say he's been moody lately, has his appearance smartened? Aftershave being worn? Could he be playing away?