I understand why you feel the way you do and in a similar situation, I too, would feel hurt, angry, and confused.
That being said, it's not healthy or productive for you to keep worrying about this. I understand that this is your best friend who is pushing you away for no apparent reason, but as others have said, this is her problem. Not yours. She's dragging herself down in a funk, but you don't have to go there with her.
Whatever is going on, whether it has something to do with the circumstances of the pregnancy, crazy hormones, or whatever, she has chosen to back off of the friendship. You made the right decision to just let her do it and not contact her anymore. As for seeing them around, going to the home church group, etc. I would just continue on as if she was never your BFF and you never had a falling out. Let her be the one to say that someone needs to change groups and if she does say that, I would contact someone at the church who can possibly help sort through the logistics of that. If she is the only one that wants you out, leader or not, others in the group can back you up...perhaps all the way to change of leadership....especially if right now she's not emotionally able to handle both leading the group and navigating the pregnancy and the baby that comes at the end of it.
As for her husband, it's very possible that he's telling her she needs to talk to you or that she's projecting things on to you that aren't your fault. He probably does want to see her continue her old friendships. The thing is, what he says to her in private is private. I know that I had some crazy thoughts when I was pregnant and my poor DH tried his best to let me know that without upsetting me too much. In the end, he was always on my side and regardless of what we discussed in private, he never went behind my back and said anything to my friends about it. I think that your friend's husband is probably doing the same thing. He's still friendly to you, so that is a good indication that he holds nothing against you, but if his wife has chosen to let go of the friendship, regardless of how he feels about it, he's choosing not to publically oppose her in that decision.
I know this is hard and I know it's difficult to see a good friendship fall away and not have the answers you deserve. The thing is, you may never get those answers and your friend may not even know why she feels the way she does. The only thing you can do is accept that this is what it is. There will be a mourning period for sure, but eventually, you'll find that things are probably working out for the best right now.
