I think it's very common to think that you are somehow protecting them more by staying as you feel you can moderate his behaviour or act as a sort of screen.
Unfortunately it's not true. They won't be able to separate out his actions, and see you protecting them from his unreasonable behaviour, they will see his behaviour and you excusing and enabling it and assume that it is acceptable. You will also be doing subtle things you are unaware of to keep the peace which are unhealthy and that you wouldn't want your daughters to repeat or your sons to expect. It's just impossible not to play out these dynamics when you live with somebody who is emotionally abusive.
When you are separated, yes they will see the unmitigated effects of his behaviour. They may well get hurt by him. But they will always have a safe place (you) to come back to where that kind of thing never ever happens. Instead of being a low level presence always, where they barely notice it and accept it as normal, it is stark and separate. They can see it more easily and process it. You are not throwing them to the wolves by allowing them unsupervised contact, you are allowing them the freedom to make that judgement for themselves. It might well be very painful for you, especially if they lean towards him perhaps in the teenage years, but it's still the best way for them, and they will come back to you - emotionally healthy support is always more satisfying, fulfilling, and real than emotionally unhealthy parenting or control. He might be "the exciting one" for a while, but children grow up and they understand that exciting does not always mean best.
All of my peers, (female, mid 20s) without exception, whose parents waited until the DC were grown to split have been in a string of and/or are still in emotionally unhealthy relationships - unsurprisingly! Because this is the script they have learned for relationships, and this is how they think things work.
Think of it this way - staying is like feeding them the lowest strength Silk Cut every day in a slow but steady stream. Low powered but still enough to build up a lining of tar. Leaving, and them seeing him, is like them smoking a full strength Marlborough once a week. Far enough apart and enough contrast to be able to taste the unpleasantness alongside the excitement and danger and coolness.
I totally understand staying if the fear is that he would actually kill them and you don't have faith in the authorities to protect them, but I would hope that is a vanishingly rare situation, and not the one the OP is in.