Why didn't Leo replace the female assistant?

Leo doesn't change female assistants because they have a very good relationship. Leo and female assistant are buddies, older than couples, and normal couples don't mercilessly dig at each other. This mode of getting along is actually sweeter than couples. The female assistant is willing to accompany him from obscurity to success. She is very happy, happy and hardworking every day. Moreover, Leo is really a good person. They get along very well, so Leo doesn't want to replace the female assistant.