Sounds like SIL has a lot to deal with and her H's attitude is making it so much harder than it should be. Reconciling is hard work, I know that even if I haven't ever done it, and after an affair it is even more so because that's one huge betrayal to forgive. Why did he bother coming back around and proposing a second chance if he wasn't truly invested?
New thread: http://www.divorcebusting.com/forums/ubbthreads.php?ubb=showflat&Number=2112303