@Myriade
I would take that as breeh of trust tbh. Yeah it's a breach of HIS trust. It's between him and his mum.
OP is free to get upset about it if that's what she'd like to do, but it's a "not my circus, not my monkeys" thing isn't it?
She is projecting an image of herself that doesnt reflect the reality. And yes a lot of people do that and give a very curated view of who they are on SM. But dont you think its going a bit far?
People post FB pictures of their babies in SCBU regularly and no-one bats an eye.
Not sure there is a time of life more vulnerable than a little baby in hospital in his/her nappy, typically with a feeding tube taped to their cheek, breathing apparatus on face, and a drip in their poor little foot/hand.... no one says a word.
FWIW I think it's revolting, my own DC have NEVER had a single picture of themselves put on social media, EVER. But it's normal these days.
An adult DM talking about the condition of her ill adult DS on her own FB page is normal.
OP can get herself worked up about it if she wants, but from what she's said, I'd suspect her partner is fine with it and wants her to lay off his mum.