Whether its just a few hours or several decades, her memory coagulates forever without degradation. She has so many memories that her perspective of time is an infinite scale, where everything that has ever happened is instantaneous in her mind. She learned from probably thousands of experiences that having only a few good memories with a person is much better than waiting for the eventual bad memories to stain them. Likely she was looking for hundreds of years to find the perfect person like him, once again, so she could do just that.
So before there was any deeper connection, before there was anything but memories of a happy time, she left him to continue his life.