Mapam - your pain is palpable in your post, and I feel and relate so much to you.
You will get through this.
Things obviously came to a head, and you made a very brave decision to get him to leave. I did the same. After the shock and disbelief, you will draw strength on the fact that you had the guts to do this. You sound a lovely mum, you're kids are your priority - as mine are to me. So remember that in order for you to feel that you two had no future, knowing that you were instigating the break up of the family, THINGS MUST HAVE BEEN VERY VERY BAD WITH HIM. So don't take on the guilt - don't blame yourself. He caused this. You have enough to cope with, without blaming yourself. You say that they won't have a mum and dad to live with. Well, there mum and dad won't be under the same roof. But they will still have a mum and dad.
You're an intelligent lady, you know, I think that an unhappy mum and dad living together, in the atmosphere you've been enduring, (suffering, more like) is not a healthy environment for kids to grow up in. Even young ones like yours will pick up on it, and it will affect them. So don't feel guilt for the kids. Let them see you (and you will) flourish and be happy again. A strong, positive happy mum is far better than a bewildered downtrodden shell of a mum. I am living proof of this. Everyone says (and said it soon after I chucked ex out) that the atmosphere was lighter, and that I was back to my old, carefree self.
My ex projected all his faults onto me. He constantly said I was highly strung, over sensitive, etc. I wasn't I was just hurt and downtrodden by his coldness and detachment. And couldn't cope with the way he constantly put me down and criticised me. He did this to give himself permission to leave - if he could make out it was all me, and that I had all these faults, that I was a paranoid insecure woman, he could justify leaving me. It took me a few weeks and a lot of helpful posts from the wise ladies on here, to realise this. But I bet you can relate to it, or you will in the future. It wasn't you - you've done nothing wrong. You are fine. He has been cold and detached and that really hurts. So for now don't try to understand it, just try to accept it. He doesn't love you anymore. Don't blame yourself for this, whatever you do. I did this, for two years before I kicked ex out: I tried everything to make him love me again. A waste of time, energy and make-up.
The next week in particular will be a rollercoaster - ride it. Cry, and take it minute by minute. I wish there was a fast-forward button, and you could be where I am now, but there isn't. So go with it, take it all at your own pace. Post on here, and we'll help you. It's like the grieving process, you'll cry, you'll feel anger and disbelief, and that awful gut-churning terror of the future. But the future is actually going to be better than the past, because you'll be you again. Please believe this.
One more thing "my family expect me to be strong". Be honest, say, "actually, I'm not coping as well as I thought I am" - and lean on them. Lean on friends, let them know that this is hard for you. You'll find that people want to help. So reach out - don't let pride stand in your way. You've done nothing wrong, you're not to blame.
Will check in later.