Sexual Twilight by Anne Herbert

'NO MAN COULD SATISFY HER. No woman could fulfill her. Lillian belonged to the oddest sexual twilight - a lesbian in love with a man. Lillian needed John, wanted John - but she wanted, she had to have, her lesbian lovers more. Like the young girl she found in a 'gay' bar, and took home to initiate into the ecstasy of homosexual love. Or the older woman with the bizarre variations on the usual lesbian love-making. When Lillian first met Cathy, it was just a casual pickup, to last a single lust-filled night. But Cathy was different - when she was finished, she had lured Lillian into the strangest sex triangle of all!'