Forgive me for bringing up past posts (not normally my style, because I can't usually remember them- lol), but here I go...
http://www.disboards.com/showthread.php?t=2015400&page=1&highlight=
In this thread, you were upset that you were not asked to be part of the wedding party. It was pretty clear that you were not thrilled that your brother was marrying this woman with 4 kids by 3 different fathers, and had been married to only one of them.
Maybe your disapproval of her was not as hidden as you would have liked? Maybe the disapproval of her pushed your brother away? Could he have felt that he was being forced to make a decision between his parents/sibs and his new family? If so, I can promise you the new family will win most of the time.
Then, in another post, when you found out that your brother had fathered a child with another woman, you seemed...hopeful...that the news would change things and maybe your brother would not be getting married.
(
http://www.disboards.com/showthread.php?t=2015809
But I think the stuff that has come out will effect the wedding and other things
Yep--I think you were a little too obvious with your disapproval and now your S-I-L doesn't want to be around you...and apparently, your brother has sided with his wife...as he should.
You need to try to make a clean start with them. If necessary, apologize for your past behaviors. Accept that your brother is married, whether you like it or not. Accept his wife and her children as your family and quit looking for something wrong in everything he does with them.