I understand your and H's struggle better - thank you for sharing that. I'm sure its not the easiest thing to talk about, yet you probably need to. That was not a clear-cut situation for you, and it sounds like you both tried hard and felt the loss deeply. Usually, when we describe sitch's with "shoulds"/"oughts"/"musts", things are more complex than that oversimplifying.
I wonder - if you forgave yourself, would it be easier to accept your baby's loss and move back to the present more fully, both with H and with your children? From your H's apology and actions, he seems to have already forgiven you.
Boy, "The Birds and the Bees" convo - you are brave! LOL re your daughter's reaction. Ha!
In terms of having another child with W, yes indeed. I'd love to. I always wanted a big family, whereas W thought 3 then 2 then 1. I'm a bit rusty now, so we'd have to practice. My motto would be: "If at first you don't succeed, try, try again!"
My motto would be: "If at first you don't succeed, try, try again!" 
