STBEH outing affair relationship on social media

[VivaVegas]

So after sneaking around behind my back for nearly a year, lying to everyone including his family and making out I'm a psycho and a crazy as she's 'just his friend' he goes public on social media, late at night presumably after a drink.
And this is a man who rarely uses social media.
Why on earth would someone do that, so disrespectful but what is he trying to prove??
I'm blocked by him but his post was copied and sent to me as a lot of friends are pretty disgusted with his behaviour.
And this is a 50 year old man fgs.
We are separated, it's very acrimonious because of his behaviour, was he just trying to spite me, is he desperate to prove he is happy.

Just ignore it. As for your friends sending the screen shots to you, tell them yes, you know about the other woman as he’s been cheating on you with her behind your back for over a year, trying to make out that you were a psycho and crazy so you would rather not hear or see about their relationship, thank you very much.

They know what his lying and ongoing denial has done to me, so they were hoping it would give me closure, albeit in a spineless way by him.
I'm glad they told me, I just don't understand what he was trying to achieve.
It's backfired but that's not my issue.