Bron, I just want to give you a huge hug. I had all this when my SiL fell pg last year: she was announcing hers just as I'd have ideally been announcing my baby (15m before I fell pg), my problem wasn't TTC but that my DH wasn't ready to TTC; still, the emotions I went through are very similar.

You're quite right in not saying a word to your family: trust me, they will all think you are the most evil b*tch who ever walked the face of the earth (even my mum, and it's not her grandchild: it's my MiL's grandchild, and later my mother's great-niece - SiL never mentioned about TTC and my cousin kept calling hers an "accident" all the way through her pregnancy). It's far, far better to have a good support group of like-minded girls. We all know that you are happy, deep down, but you have other stuff to deal with first and believe me, you do have to deal with it.

You're quite right, it's not fair, and nothing anyone can say will make it fair. There will be days when you don't even want to think of her: don't. If you have to avoid family things, do so. Say you're ill or something - this could cause a mental problem, such as depression (again, trust me on this) and your mental health issues are just as important as her baby. Call-screen when you can't cope. You will never feel happy for your SiL while you try to force yourself to: I want you to buy her a congratulations card if she is pg and then forget about her for as long as it takes. OK, the card won't be easy to buy but I do know you'll be pleased you did it in a few years.

My SiL sounds similar to yours; she ended up extending her maternity leave and now is a devoted mother. Just because she didn't do things "my" way doesn't make her a bad person. It was very, very hard to tell myself that before I fell pregnant, but I'm glad I did manage to finally be happy for them without any extra feelings going on before I fell pregnant.

Just wanted to say that getting "over it" isn't easy, but getting through it is do-able, and I really hope you fall pg very soon so you can share your pregnancy journey together.

Best of luck to you.