My sister in law and I are best friends. She split from my DB around the same time I left my abusive ex husband. We have always loved and supported each other. My brother has been an enormous dickhead when it comes to taking care of his own children, he's put his own relationship over his children (niece is 12 and nephew 8) SIL didn't work when they were together but had to when they split, as a result I look after niece and nephew every Sunday and cook dinner for them all (they're at mine and means SIL doesn't have to cook). Recently I work do came up, it's a weekend away and SIL said she'd be happy to have my kids for that weekend. Great, I tell my boss I can go and he's booked me two nights in a hotel in London. Now SIL is making things very akward, she's stresssd about who will look after her children that Sunday. I wish she'd said all this before my boss forked out, I would've stuck to our arrangement if she'd just said, now I'm a bit resentful. I don't expect anyone to look after my children, they are my children after all and also think my useless brother should pull his finger out of his arse. I'm gutted to miss out on the work thing but even more gutted that my SILmade things so akward when I go out of my way to make things easy for her (and not just making up for my fuckwit brother, I genuinely love this woman, she's my closest friend)