DS is 10.
Since age 5, he's been best friends with a girl in his class, let's call her Mia (not her real name). They've spent 5 years being each other's best friends. And in that time I've become really close to Mia's mum. 5 years of playdates, park after school, entire Sunday afternoons spent together, going out for lunch at weekends as families, I've had them round to mine as a family and hosted them on numerous occasions. Bought lovely birthday presents for them as they have done for us. What I'm trying to explain is, we ensured been close for 5 years.
A few months ago, out of the blue, DS came home from school upset saying that Mia had suddenly started saying mean things to him like "I hate you". "Every one in this school hates you". "Your face makes me want to vomit". "You've got no friends". All this was out of the blue. There had been no fall outs or anything.
I talked to Mia's mum and told her that Mia had been saying these things to DS, and I asked if there was a problem I didn't know about. Mia's mum said "Mia simply wouldn't say anything like that. Your DS is lying". She then called Mia over and said "Did you say these things?" Mia said "No" and Mia's mum turned to me and said "See. She says she didn't say it." Then stormed off without saying bye and made it clear she was furious with both me and DS - she literally glared at him with fury as she stormed off. He became worried and said "Why is Mia's mum angry with me?".
The next day at school, Mia ran up to DS and said "You're a snitch!!! I hate snitches!!! I hate you for snitching on me!!!". DS said "You said those things to me Mia, it really upset me, I thought we were good friends, I'm not a snitch, I just told my mum about it". Mia gave him more horrible personal insults and ran off.
The insults carried on for the next few weeks, with DS coming home regularly telling us that she was saying really horrible, nasty, spiteful, personal mean things to him at school, and she totally dumped hanging out with him and switched to a new friendship group of 'cool kids'. They are much older in their ways and their attitude than DS is, much more streetwise, sarcastic, mouthy, argumentative, trendy 10 year old boys walking round in teenage style clothes like ripped jeans and oversized skateboard tops and beanies with smartphones and using a lot of swearing in their general chat (I see them hanging around the park a lot outside of school). DS is nothing like this, he's still very much a child.
After a few weeks of Mia saying spiteful things to DS at school, I spoke to their class teacher about it and told her everything Mia was saying and I asked her to see if she could help with trying to sort out what was going on, because DS was coming home in tears about it. I imagined the teacher would get the 2 of them together and talk it through, knowing that they'd previously spent 5 years as best friends. Instead, the teacher spoke to Mia alone and came down like a tonne of bricks. At pick up, she said to me "I've blasted Mia today for what she's said to your DS, I'm coming down on her like a tonne of bricks and I've told her I'll be watching her closely and I've told her you've spoken to me about her behaviour so that she can't lie about it and so that she knows we all know".
From that day on, Mia has never said another thing to DS, but equally she now just blanks him. He says "She looks through me at school like I'm air".
Likewise, Mia's mum has stopped talking to me and either blanks me on the school run or gives me sliitted eyed evil stares.
We've both lost good friends. Long standing friends who became family friends that we spent a lot of time with. Mia's mum constantly referred to my DS as "Mia's bestie" from age 5 to 10.
DS is asking me how it went from him and Mia being best friends, to Mia turning against him literally overnight without anything bad having happened between them, no fall out, nothing.
He's asking me about it a lot and says he's really upset about what has happened and that he thought he and Mia were close friends.
I don't know how to explain things to him, because I literally don't get it. I don't understand what has happened.
I've never encountered anything like this before!
AIBU to feel upset that we've both lost close friends without either of us having actually done anything wrong?
How do I advise and explain to DS when I myself don't understand Mia's behaviour after years of them having a happy friendship where Mia used to actively seek out and love my DS, and ditto Mia's mum towards me?