Sorry I couldn't reply to your welcoming PM, Daisy- I don't have enough posts yet to be able to!
I often feel SO much worse when I'm tired- it's impossible to think clearly. So certainly don't make any big decisions until you've had some sleep.
I don't see you separating as a failure at all, although I can see why you might. I've done a crash course on addiction over the past few weeks, as you know, and one thing I have learnt is that however much you might love someone, you can't change FOR them.
I think you owe it to yourself and your children to do whatever YOU need to do to preserve your health and safety. If that means separation, then so be it. Don't be misled into believing YOU have split up the family, though.
I told my husband he could either have an active drug habit or a family, he couldn't have both.
Thinking of you.