On people moving out of town.

When a friend of yours is leaving your home country, it feels like they are going to leave your life forever. Even when you still hear from them. Even when they do come back at times. I'm not sure if it's about the lack of communication or the fact that they are practically living a new life that it feels like they have left you.

Even if it's just for a year.

A she, who is an old friend since elementary school, who was close to you, as close as twins could be - people do actually mention that you two do look alike. Alas, the two of you grew apart, without you knowing why.
Several years gone by, and you've heard that she went abroad. Hearing that, you were puzzled by your own feeling, questioning "Why do I feel like I've lost her?".
Another year gone by, and she came back. Did you find the answer to the question? No -- it multiplied. "Why is she different?" "What happened to her?" "Why isn't she the same person that I've once known nine years ago?"
She is not the same her. Neither is him. They have become slightly, unknowingly different.

The feeling of losing someone you'd never thought you'd feel bitter upon losing.