Complex sentence: She got to know Per Böklin, a principal at a school in Kristianstad, in the 1830s, who gave her private lessons and became her friend; he asked her to marry him but, after several years consideration, she declined.
Split into simpler sentences: She got to know Per Böklin, a principal at a school in Kristianstad in the 1830s, who gave her private lessons and became her friend. He asked her to marry him but, after several years consideration, she declined.