I finally found a copy of this 1973 movie. James Caan plays a sailor who lands in Seattle and his paperwork gets lost, fallen behind a file cabinet. Consequently he's stuck in Seattle for what turns out to be 6 months, can't ship out, can't get paid.
He visits a prostitute (Marsha Mason) in the first days, and because he's stuck here, he ends up getting embroiled in her life. She has an 11-year old half-black son, she's pregnant, her son is rebellious, she has no health insurance. He ends up marrying her so the Navy will pay for her childbirth and her other son's dental care.
It's a sweet, gritty love story about clashing worlds, and kindness, and reaching across the void to touch another person. Seattle in 1973 looks very recognizable, although the Navy never docked ships at the freight terminals. The Seattle waterfront used to be full of adult bookstores and porno theaters, though they're all gone now. The kid who plays her son is great in this. Marsha Mason got an Oscar nomination for her role. Unfortunately, the music (by John Williams!) is terrible and overloud, and features several songs by Paul Williams (yech!)