I agree with NQ. Try and limit what you say to your family and his family. Although they have really good intentions, I have found that their advice is completely against DBing.
I am really close to my H's sister. She truly is the sister that I never had. I was there for her through infertility and we were pregnant at the same time last year. We pretty much talked everyday. I still talk to her more than H talks to her. However, we make it a point to talk about everything else besides my H and our M. I have gone out to eat with her and we even went to the movies a couple of weeks ago. We talk about our kids and work and mutual friends. There is a white elephant in the room, but we are both ok ignoring it for now.
Since H refuses to talk with her about our sitch, she does ask every once in a while how things are and where H is. I never bring it up. But if she does, I dont bash H or talk about my sadness or our M. I just tell her that I am doing well and have been busy (talk about stuff I have done with the kids, or yoga, or signing up for the 5K or visits with friends). I figured that if H ever asked his sister for info on me, I really only want her to have positive stories of me to share with H.