Ex left me for OW 18 years younger

[Applesandpears1806]

My STB EH of 18 years has left me for the OW he had emotional(he says)affair.
I've posted on here before at times about things,but now,after living in the same house together separated for the last 7 months he's moved in with her. We have a DS who is 8.He abruptly moved out on the 4th, into an Air Bnb with her for a week. Within days they've viewed a house,put up a years plus of rent and are moving into it. He's 39 she's 22!
It's laughable in a way to me,but now I'm facing the prospect of my son meeting her at some point which I will have to deal with.
Anyone else had experience of this or something similar?
I want to be the better person about it all,and I'm trying. The most important thing is my son's happiness. But I just cannot believe his behaviour,and feel he's so deluded about his life choices. What a fucking idiot! I'm struggling to keep my mouth shut. 🤦‍♀️

I hope you're doing ok @Applesandpears1806 I'm sure once they're living in "domestic bliss" the shine will soon wear off for the 22 year old.

Also, I agree with everything that @FloralCrown said, especially this:
Definitely get a clean break order or he can potentially come back for more.
Also, make sure he gets a pension valuation - he may well be being "generous" with the house equity because he has a large pension pot that he doesn't want you to touch and that is far bigger than the equity amount.