The first thing you need to do is check the laws in your state or province. Some states allow legal separation and some states do not recognize it.
The second thing to do is to find a L. Even if your state does not recognize legal separation, you can file for D and get temp orders to protect yourself and your kids, and then do nothing to move the D forward until you are ready.
Regardless of which way you go, you can start separating your finances now. For example, open your own checking account and move your direct deposit to the new account. Remove WH from any credit cards where you are the primary card holder and also remove yourself from credit cards where he is the primary card holder. Move 1/2 of your savings and investments into accounts in your name only. If you are staying in the family home, change the utilities to your name, if possible.
Good luck and (((hugs)))