I am so sorry! I know this is a big blow. I can somewhat relate, since my H had a pregnancy scare with his OGIRL this last winter.
It will be hard on your boys at first. I think they will need the steadiness and security of their mom even more in the coming months. Just try to focus on them and you for now. There is truly nothing you can do for H now.
Maybe this latest development will be just the thing for you to really REALLY detatch. I know when I heard my H might be a dad again, my very first thought was for my kids, but my next thought was anger! and sometimes it takes a little bit of anger to detatch.
I am here for you, and if you want to get together, just drop me an e-mail. My schedule is pretty light until fall.
Take care, SG
Survival Goddess "The most common way people give up their power is by thinking they don't have any." -Alice Walker