I think this thread shows how different people are, and how each of us have experiences that colour our responses to the same information.
I read 'Apologies if I'm not myself but my son died yesterday.' and thought 'Jesus, how flippant.' Someone's son died and they used a phrase like 'not myself'? The heart's been ripped out of you, and that's how you present on social media? The start of the sentence could also be used for not having had a great night's sleep, or worrying about how to pay an unexpected bill, or waiting for a call back from a doctor about a test result. Not for the enormous life-changing reality of your child dying.
I also read 'my so-called friend' as being a response to 2 people having such astronomically different responses to similar significant events. The death of a child provokes such instinctive responses, how could I be friends with someone who responds so fundamentally different to me? Also, have they not understood the journey I've been on for the past 14 years? Have they been astounded by my responses? Have their reactions to my grief been genuine, or have they quietly judged me as my response to a similar situation is very obviously so different to theirs? Was this friendship real?
But then my reading of the OPs post is also coloured by my own experiences, and the grief I carry with me. Because that's the thing. Grief is an awkward-shaped sack of shit you carry around with you every day. It doesn't matter if it's 24 hours, 14 years or decades longer. It's still shit. And you still carry it with you. Everywhere. Every, single day.
With time you get better at carrying it with you. You get better at balancing the load, but life will always throw you a curve-ball (sometimes in the shape of a social media post), and you lose control of that awkward-shaped sack of shit, and the shit gets far too real for a while.
And when that happens, it doesn't matter how long it's been, you get flung back into that awful raw emotional state of death and loss and grief. Logic and empathy and compassion don't fit with that state. It's just full of hurt and pain and self-focus. And that's okay. Because that is grief. Sack of shit grief.
OP, I hope your pain eases.