You answer many of your own questions here, IMO. The visual and narrative language of noir takes root from two parallel but opposite but gravitationally aligned impulses--tragedy taken from the gods and put into the household (what ChiO likes to call "domestic melodrama"), and the violence (physical and emotional) that breaks free of societal restraint as it is often manifested in various forms of "forbidden activity."

It's clear that in the 40s, these impulses merge in cinema around the world--building on what occurred in France in the 1930s. "Melo-noir" is a fascinating stew with a lingering aftertaste, and you could make hay by taking your approach here (especially as it has been extended into a discussion of JOHN & IRENE) and applying it to masterful melo-noir variations from that same year elsewhere: THE PASSIONATE FRIENDS and THE SMALL BACK ROOM in the UK, LES EAUX TROUBLES in France, and...well, I'll let you find the American analogues in 1949 for yourself...