Andrew was very unhappy in his last relationship, and he did not mourn for Lise as much as the typical widowed husband. He also decides to pursue Natasha on a whim: simply because she went and talked to her cousin before Mademoiselle Bourienne. This decision is strongly out of character for Andrew, as his decision is based on entirely false logic.
Natasha falls for Andrew pretty quickly, and seems happy about the idea of marriage. She tells her brother that “Oh, if only [Andrew] would come quicker! … I am growing old” (Tolstoy 460). However, in book 7, she says that “I know that I shall never again be as happy and tranquil as I am now” (Tolsoy 455). Natasha is clearly sad about leaving her happy childhood behind.
Clearly neither Natasha nor Andrew are 100% sure of their potential marriage, but everybody gets cold feet, right?
Do you think Natasha and Andrew's regards about their marriage are normal, or does it show the marriage is doomed to fail?