Actually, the most terrible thing he did as a father, was to be so "distant" and UNinvolved in raising his SON, his only son, and thus allowed him to become a momma's boy and it's always the momma's boys that have a rose-colored, sugar-coated view of the true nature of wimminz it's the momma's boys who try to make a housewife out of a sociopathic whore.
That stupefied look on Martyn's face when he sees his "loving" fiancee' getting her BRAINS shagged out THAT fatal naivete' is on dad, mostly, and mom a bit too.

Yeah. If you read the book, he pretty much says that. But when Martyn dies, he is consumed with pain over it.

And knowing this, he goes looking for Anna again and tries to be with her again.

I felt sympathy for him during the conversation with Martin at Martin's office. It seemed as though Stephen was lacking aspects in his personality, especially empathic ones, that came naturally to others like Martin.
Also immediately after Martin's death it is he who rushes to his son and stays with him until the ambulance arrives. Anna leaves. As though her work - to damage others - has been done
my vessel is magnificent and large and huge-ish

Yep. Not just the scene in the kitchen.