I have seen many people express dissatisfaction with the ending, which I understand. For many young people today, the concept of enduring love and the difficulty of moving on after losing a loved one may be hard to grasp. However, having worked in the healthcare sector with the elderly for many years, I've encountered numerous individuals who have remained alone for decades yet still speak of their deceased spouses as if they were alive, but still having lived a full and rich life. In my view, this isn't necessarily unhealthy. Some people simply struggle to move on, and the reasons vary widely.
For some, there may only be one true love. The difference lies in whether one's inability to move on is accompanied by conditions such as depression or other mental health issues that impede their ability to live a fulfilling life. In such cases, I agree seeking medical assistance is crucial.
However, in the case at hand, there's no indication that the protagonist is suffering from any mental health issues. From what we observe, she maintains friendships, attends school, pursues her passion for writing novels, and leads an active life. Yet, romantically, she remains fixated on the person she regarded as the love of her life. Whether this will change in another five years is uncertain; people's experiences and responses to loss vary greatly.