Second Gone With the Wind!
Not sure if it's exactly what you're looking for but Neville Shute's books have some touching romantic tones - very subtle, definitely no sex and written in the 40s so barely a kiss. A Town Like Alice and Requiem for a Wren.
The Camomile Lawn by Mary Wesley is a little more racy in parts (there's also a TV adaptation available to watch for free on 4OD)