Yes, Mrs. Pratchett, sad. Interesting that you noted he said it was a long story, then he told her a very short story. Fleeing to bed in between says it all.
Also agree with Phillis, I would have told his mother right then. You have to speak up to the people around both of you as soon as something this traumatic happens because you can bet he will spin this thing until you are cast as the villain. You can take that to the bank.
He felt smug enough to high tail it to bed to consider his options knowing you would be downstairs sitting primly not saying a word and observing the ettiquette of entertaining his mother and minding his children while worrying yourself to death over this loser and how to save your marriage.
It's not normal what he did and is doing. It's not what decent husbands and fathers do. You can't save something that is not there. He is doing his own thing, a particularly vile thing, and has done for a long time. His mother needs to know, his so called friend's wife needs to know she and her husband have been put into this little story as the excuse.
Broadcast it far and wide (to necessary people, you know what I mean) while it's happening. He needs to be brought up short. He's awful smug, Op. Pay no attention to his spin. Have a little faith in yourself. You're not going to lose him if you act boldly, he's already gone and has been gone. Do the opposite of what he expects you to do and do it now.
That screenshot...this is not one of those little spats or misunderstandings or ups and downs in a normal marriage...I don't advocate it lightly--this is a genuine L T B