Should we just leave her to it?

hiya, im sorry but there is nothing you can do to help your sister if she does not want your help,you have to let her do things her way,and her finding out about ever think her guy is doing behind her back will all come out in the end.it always does.your main worry is your niece,and the new baby when it comes.if you know there are drugs being used in the house were the kids are,then you need to tell the police or social services,its for the children's sake.also if he starts getting of his head on drink or drugs the kids are on high risk.that is all you can do.and hope he gets caught with drugs on him,he will go to jail,and that could wake your sister up,and she might not have him back.x