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。

Give me a call sometime.

有空给我打电话。

Call me sometime.

有空打电话。

Let's get together again sometime.

我们什么时候再聚吧。

Let's keep in touch.

保持联系。

Don't forget to write.

别忘了写信。

Please give my regards to your family.

请代我向你的家人问好。