The friendly young ladies - Mary Renault

Elsie, sheltered and naive, is seventeen and unhappy. Stifled by life with her bickering parents in a bleak Cornish village, she falls in love with the first presentable young man she meets -- Peter, an an ambitious London doctor. On his advice she runs away from home and goes to live with her sister Leonora, who escaped eight years earlier.
But there are surprises in store for conventional Elsie as her sister has a rather bohemian lifestyle: not only does Leo live in a houseboat on the Thames where she writes Westerns for a living, she shares her boat, and her bed, with the lovely Helen.
When Peter pays this strange menage a visit, turning his attention from one 'friendly' young lady to the next, he disturbs the calm for each of them -- with results unforeseen by all . . .
Mary Renault wrote this delightfully provocative novel in 1943 partly in answer to the despair characteristic of Radclyffe Hall's the Well of Loneliness. The result is this witty and stylish social comedy.