“One Fine Morning” sounds an innocuous title for a grownup relationship drama — destined, perhaps, to be confused on streaming menus with the George Clooney-Michelle Pfeiffer romcom “One Fine Day” — and in a sense, the mellow, melancholic cinema of French writer-director Mia Hansen-Løve is its own kind of comfort viewing. But as with many facets of her filmmaking, there’s a smarter, sadder, more literary undertow to the title’s sunny simplicity. “Un beau matin” in French, it’s lifted from a haunting poem by poetic realist Jacques Prévert, which describes in plain imagery the conflict of facing absence in your life, all while pretending there’s literally nothing there.

Suffice it to say, then, that Hansen-Løve’s latest is not a romantic comedy, except in the interludes when it is. At no cost to its calm, loping pace, “One Fine Morning” is about many things at once, in the way...