Sounds like you have a ton of things going on around you that are really stressing. Just keep trying to take care of yourself. I know it is hard right now, but you have to take care of "you".
Are you close to his parents? I say that, because in my sitch, I have been very close to my in-laws. I have spent more time with them in the last five years then my own parents and have developed a great relationship. Since the A came out in the open, there has been zero contact between us at my W's request. They have been very hard on her and are extremely upset. I just wish I could reach out and tell them how I feel and what my plan is for working though this. I know in the end, that these are her parents, and I need to respect that. W is grasping for their support right now and not getting it. They feel that if I contact them, it will be us against her. I understand how she could feel that way.
I do understand how the grandparents would want to see the kids. I think that if your relationship with them is okay, I would try and make it work for them to see the kids. If they know the situation, I know they probably fear that you will take the grandkids away from their family. Does that make sense? My W told me that my in-laws feared that I would get upset at the A and take a strong road towards full custody. Just something to consider.
In the end, I see this as the kind of A that will fizzle out over time as MWD suggests. I wish my sitch was the same in that regard. I really see some positives on your side and look forward to your updates.
Keep your head and up and take care of yourself! Detach and GAL! These two things could do wonders in your case. Show him what he is missing.
Me - 33 W - 33 S - 9 months M - 3 years T - 5.5 years Bomb - 12/14/10 ILYBNILWY PA discovered - 1/18/11 PA began - 3/22/10 Separated
