Dear Alex,亲爱的亚历克斯：
I'm writing to show you my gratitude for your kind help with my English learning while you are in my country. 我写这封信是为了向你表示我的感激之情，感谢你在我的国家时对我英语学习的帮助。
It was a beautiful and unforgettable memory that you were always sparing no effort to encourage and inspire me whenever I was in trouble learning English.
Thanks to your help, I've made great progress. I'm feeling at a loss hearing that you are returning home. I've been expecting to stay in frequent contact with you.每当我学习英语遇到困难时，你总是不遗余力地鼓励和激励我，那是一段美好而难忘的记忆。多亏你的帮助，我取得了很大的进步。听说你要回家了，我感到很失落。我一直希望能经常和你联系。
Have a good journey!祝你旅途愉快！
Yours,你的,
Li Hua李华