Chris, a similar situation happened to me - we were 'best friends' and then worked together with a small cottage industry business dyeing threads. The cracks began to appear as she grew in confidence but it felt as if it was at my expense. She patronised me, made belittling comments and expected me to laugh at them when they made me feel small and ridiculed. It's a subtle form of bullying - chris999, it doesn't matter how oversensitive you are, how much of a worrier - this is still bullying. It's very tricky working out how to deal with it though. In my case, she told me she didn't want to work with me any more - BY EMAIL, not in person - and the resulting fallout was horrendous as we had to split all our stock and she got her OH to come round and bully me into doing it all by the date SHE set. That was over 5 years ago, and I've moved on since but it's left its mark.
In your case, would you be able to ask her out to coffee or suggest a meeting with her, just the two of you? You could then tell her that you've noticed that you feel your friendship has changed a lot recently and you're wondering if anything has happened to cause that. Tell her how much you valued what you had and how sad you feel that things seem so different, and is there anything you both can do to work things out and make it better. You then aren't accusing her, which might make her angry and defensive, but diffusing the situation a little - whilst making it clear that you feel sad and that you miss what you had.
It's horrible feeling excluded - and I'm sorry to bring up my experience again but we went to the same textile groups and I was the one who had to withdraw from them all to avoid awkwardness with mutual friends and acquaintances. She had also taken up with someone else and they had become best friends. And you're right: it's very much like the school playground. People are complicated beings, aren't they? I do sympathise with your predicament and I'm curious to see what other advice you get on Gransnet. I'd definitely consider talking to her though if you can face it. Youd then have the moral 'upper hand' in that you aren't seeking to blame her but looking together for a solution.