求翻译：上课时他非常严肃，课后他陪我们打篮球，我们非常开心。周末他带我们去爬山，和他在一起的日子很开心。可他要回国了。那天，我们班的同学都来替他送行，看着他离开。是什么意思？

He is very serious in class, he accompanied us to play basketball after class, we are very happy. He took us to climb over the weekend, and his days a lot of fun together. But he had to return home. That day, students of our class to send off for him, watching him leave.