I had a friend like this a few years ago and it took me a long time to realise that her eventual treatment of me wasn't actually unusual. In the beginning we became close very quickly - she was charming, funny (but looking back, usually at the expense of someone else) and lived a seemingly glamorous lifestyle. She was overly generous , would do anything for you, and I'm ashamed to say, I was completely taken in by her for a while. It was all absolutely fine until a couple of months after I got married (she even lived in my house and drove my car while we were away on honeymoon!) and I got a promotion at work. We worked together and had been at the same level although in different departments. I realise now she must have been resentful that I'd been promoted before her as I've since found out from other friends, that the character assassinations she did on other people, dressed up as humour, she did the same about me. When I got pregnant it got even worse and she went from barbed comments about baby brain when we were in meetings together in front of colleagues, to completely cutting me dead - no acknowledgment at all, at work or otherwise.
By that point she'd also been promoted and it was difficult because there were still quite a few people who couldn't see what she was like, a bit like I had been earlier in our friendship. I had to keep a dignified silence about how I felt and what I knew she was like because I didn't want to come across as the one bitching - she was clever about protecting herself and I knew if I said anything about her, I would come across as the one in the wrong. She'd already turned another friend against me and I've since found out from other friends she also tried to turn them against me too. In a way she did me a massive favour as I know who my friends are now - they really struggled with telling me as they knew how upset I had been about the whole thing. I couldn't understand how our friendship had gone so wrong, and I didn't know what I'd done.
Luckily, in her bid to get fast promotions, she left the place we worked together for another promotion. Once she'd gone, it was like a pall had lifted. Unbelievably, I found out that NO ONE could stand her either, even her seniors. That just made it all the more staggering how she'd managed to get so far.
I'd kind of got over it and we hadn't been working together for a few months when my mum died. She knew this as I knew my colleague who was still working on a project with her, told her. She knew my mum, got on well with her, and she had come with me to stay at my parents one weekend. The fact she unfriended me on Facebook within a week of finding this out floored me. It's hard to accept that it was deliberately callous but I can't think of why else she would have done it at that time. She calculated the timing and effect of everything so it's unlikely it was random.
Anyway, I've heard she's moved jobs four times now in nearly as many years and has moved away from the area so I won't have to even see her. She's got a very senior position out of it but I can't help feeling she will keep doing the same thing and at some point she will get found out.
For a long time I thought I had done something 'wrong', but I now realise that she's done it to pretty much all her friends who can't offer her the lifestyle she wants. I thought she was joking but she once said, when we were still friends, that once I had a baby, we could no longer be friends
She doesn't have any of the friends in her life she had when we were friends so I can only imagine she's cut them out in the same way.
In a way, although it was a horrible thing that she did, I'm glad I've had the experience of finding out more about friendship, I'm less naive about people than I was and I've learned who my real mates are.