I'm in search of the title of a novel I read in the '70s. A man falls asleep and each night lives a full lifetime. He realizes he has awoken in the present day when sees a white curtain blowing in window.
The business about a man waking up and seeing a curtain waving in a breeze makes me pretty sure that the story you're remembering is “Mind Partner” by Christopher Anvil. The text is available online. The protagonist repeatedly lives out a full life and dies, only to wake up in the same room. E.g.
He breathed his last breath in satisfaction.
And woke up lying on a bed in a room where a light drapery blew back at the window and the morning sun shone in, and his clothes were folded on a chair by his bed.
This could be The Dream (1924) by H. G. Wells, although there is only a single dreamed lifetime actually recounted in the book. Most of the books is spent on a description of this dream. In the epilogue, the narrator, Sarnac, uses the dawn light leaking around the curtain at the entrance to his room as a metaphor for his awakening back in his own native time.
From the plot summary, per Wikipedia:
In circa 4,000 A.D., a biologist named Sarnac is taking a holiday among mountains and lakes with his lover, Sunray. With four other holiday travellers, they visit some 2,000-year-old "ancient remains [of war dead] that had recently been excavated" in a nearby valley. A little later, after a brief afternoon nap, Sarnac awakens from "a very vivid dream." The rest of the novel consists of Sarnac's recounting of the dream, with occasional discussion of its particulars with his companions. Sarnac's dream brings with it total recall of the complete life of Harry Mortimer Smith. Smith's life and the institutions that structure it are the subject throughout the novel of a running commentary from the point of view of the achieved Utopia of 2,000 years later.
Harry Mortimer Smith was born in 1891 or 1892 in the fictional town of Cherry Gardens, in an area bordering the South Downs on the southern English coast. His father is a greengrocer who has trouble supporting his family because of the ignorance of birth control. He profits from the sale of produce from the nearby estate of Lord Bramble, where Harry Mortimer Smith's mother's brother, Uncle John Julip, works as head gardener.
Harry unwittingly exposes this theft when he is sent to work at Lord Bramble's estate, and as a result his uncle loses his job and comes to depend on the Smith household. Uncle John debauches Harry's weak-willed father, leading him to yield to the temptation to drink and bet on horses. The only person in the household that Harry esteems is his older sister Fanny, whom he helps run away to rejoin a lover in London. Harry's parents are scandalised by Fanny's sudden departure; shortly afterwards Smith père dies after being struck by an automobile.
Harry and his sister Prue go with their widowed mother to a boarding house in the central London district of Pimlico run by Matilda Good, a friend of the family. Wells was proud of some of the minor characters he sketched in this part of The Dream.
By chance, in London Harry reestablishes contact with his sister Fanny, who has become the kept woman of an important publisher. This connection enables Harry to gain employment at Thunderstone House and the publishing firm of Crane & Newberry, where his star is still rising at the end of his life. In this part of the novel Wells analyses the importance of and limitations of popular publishers in the years before the First World War.
The conclusion of The Dream is chiefly concerned with Harry Mortimer Smith's love life. Just before going to fight in France he meets Hetty Marcus, the daughter of a farmer. They marry, but when Harry discovers that Hetty has been unfaithful to him in his absence and is carrying another man's child, he divorces her—despite the fact that he is still deeply in love with her. Wells uses the occasion to comment on English sexual mores of the day: "We had no sexual education at all, only concealments and repressions. Our code was still the code of jealousy—thinly disguised. The pride and self-respect of a man was still bound up with the animal possession of women—the pride and self-respect of most women was by a sort of reflection bound up with the animal possession of a man. We felt that this possession was the keystone of life. Any failure in this central business involved a monstrous abasement, and against that our poor souls sought blindly for the most extravagant consolations. We hid things, we perverted and misrepresented things, we evade the issue."
Harry Mortimer Smith soon marries a woman who works at his place of business. They have a child, and his career prospers. But he becomes involved with Hetty again, and his life is abruptly ended in the early 1920s when he is murdered by Sumner, her jealous husband.
In an epilogue, Wells's characters discuss inconclusively the possibility of human immortality and the possibility of memories surviving death.