Thank you so much for all your comments and your support - it means a lot to me.
And you're right about how supportive my family are. When I mentioned my brother's news to my mother - it was rather tentative, since I didn't know whether he had told her yet, so I just said, "Have you spoken to ___ and ___ yet? - her instant response was, "Yes - it just gets harder, doesn't it?" I so appreciated the fact that, although I know she'll be excited to have another grandchild, I didn't have to pretend with her. I hope they all know that I am genuinely happy for them - I'm sad for me, and the timing sucks, but I don't begrudge them their happiness in any way.
Anyway, I may not be around much over the next few days - my US brother and SIL and their seven children are staying with us until Monday. I've managed to find bed space for everyone, and have bought a mountain of food - when the woman on the cash desk in Costco saw my trolley, she instantly offered me executive membership! It'll be exciting having eleven people for three nights in a house that only has one bathroom, but I'm sure the neighbours will help us out if there's an emergency!
Have a great weekend, and if you're in the UK - enjoy this beautiful sunny weather. (Also, please think of me tomorrow - as well as having my hyperfertile brother and his family staying with us, we're going to Niece #4's christening tomorrow, and it'll be the first time I see my little brother and his wife since they announced their news. Could the weekend get any more child-centric?)