Caspar had never apologized to a woman he dated his whole life! Even Katia, who was his fiancée for 50 years, was very lenient and she forgave all his unpleasant actions. He knew that he had an irresistible charm, and he had seen countless women throw themselves at him. Katia never protested or left him just because Caspar was having fun with other women.
What made Katia finally decide to leave was because Caspar kept her hanging. After so long he never took the last step to marry her. Indeed 50 years was a long time and Katia couldn't stand it anymore.
Caspar did not mean to hurt her, he simply could not bring himself to commit to her because he realized that he didn't actually love her.
Caspar's parents who died together during World War 2 were married for more than four centuries and they were a perfect example of true love. They had known each other since they were children and both became Alchemists in their early 20s.