Details changed as outing.
So DS (6) has a friend (F) who he has known since babyhood and adores, and when the two of them are together, they are lovely together and inseparable. I really appreciate this, as DS is quite quirky (he is dyslexic and probably has ADHD) so making friends is hard for him.
Whenever F comes to play, his mum (B) comes with him. B mostly spends the duration of the playdate gossiping and complaining about minor things that other mums or their kids have done (I.e: if someone else's child has experienced some minor misfortune, i.e: vomited or soiled themselves, she laughs about it, or if another mother has experienced some form of good fortune that she is jealous of, she complains that it's not fair...etc). I nod along without commenting and then change the subject, but she never gets the hint.
When the boys became friends, she didn't openly gossip to me, and we talked about our personal lives, and I told her private things about myself that I wouldn't have had I known she was a gossip (i.e: about my brother being a drug addict, and my catching an STD from an ex). A different friend with older children, C, tells me that B has been telling people my personal business. This makes sense, as suddenly other mums who I don't really know, but who B talks to, seem to actively stay away from me and DS, and give us dirty looks when we pass them.
It's hard, as neither boy really has any other friends outside of school, and B is always reaching out for my DS to play with her DS, and the boys adore each other.
Aibu to stop seeing B? As B insists on always coming to visit with F, this would mean that DS would have to stop seeing F as well. They don't go to the same primary school or clubs, so that would be the end of their friendship, which I would feel bad about.
YANBU- stop seeing F and B, thereby ending the only friendship DS has outside of school
YABU- suck it up and keep seeing F and B so your son can still see his friend