As often happens with people who consider themselves damaged goods, he mistakes her affection for gratitude (and then it hurts too much to be around) and she thinks his kindness must be platonic (because he's always dodging her expressions of affection) and it's stupid, but it's stupid in keeping with human psychology, not narrative contrivance.

And by your account the scripts establishes this right from the start with her fear that telling her fiancé of her pregnancy would amount to emotional blackmail, and his downplaying of her rescue as merely due to his dislike for cops. I can easily believe that both are the kind of people so worried they’ll put others on the spot that they end up circling around and playing head-games anyway.

I can see why the subsequent plot would lead to screams of frustration.

Given that apparently a lot of pre-Code scripts were developed by remixing the plots of two or three earlier movies with good box-office records, perhaps this was an example of that method failing; or alternately, perhaps the script did not anticipate the on-screen chemistry between Harding and Brook, and on the page his character would indeed have worked as the “platonic friend” role.