Before you talk to him again, think through exactly what it is you want, and exactly how you will get there.
Step 1 - Get an appointment with a solicitor to find out your legal rights. This is hugely important, because he will try to tell you that you'll get nothing etc, when it's simply not up to him.
Solicitor can help you with when to do what. Take copies of any/all bank statements/ mortgage info/ savings etc with you. Remember, you can still be legally separated and living in the same house, so you'll be able to claim benefits.( If you've a joint bank account, you need to open your own account and have any wages/child benefit etc paid into it from now on. You could also remove half of what's in the joint account to put into your own also.)
Once you know your rights, and have your own bank account etc, then it's just a conversation, which is best tackled when the kids are not there. (But if you're scared what his reaction will be, either do it somewhere public like a walk in the park/coffee shop or have someone else there in the house/garden when you tell him e.g your parents.)
e.g You know we haven't been happy for a long time, and I think it's best for both of us to divorce. I want you to move out on Friday night when the kids are at my Mums. It would be better for everyone if you stayed with your parents until the house is sold, because the kids have school etc, so they need to stay here in the house for the time being. We can tell the kids on Saturday afternoon, because we've nothing on and will be free to tell them, answer their questions and comfort them afterwards. We can organise a regular contact schedule for you to see the kids. I have seen a solicitor, and they are proceeding with divorce proceedings.
Just keep it factual, and don't be afraid to tell him what you want. It's up to him how he reacts to it.
You CAN do this ! Once you begin, the forward momentum builds, and it gets easier.