I'll miss you. 我会想你的。
I wish I could go with you. 我真希望能和你在一起。 Please give my regards to your family. 请代我向你的家人问好。 You must come back. 你一定回来啊!
Give me a call sometime. 有空给我打电话。
Let's get together again sometime. 我们什么时候再聚吧。
Please write me (a letter). 请给我写信。
I'll write you (a letter). 我会给你写信的。
Let's keep in touch. 让我们保持联系。
Don't forget to write. 别忘了写信。