●暂时无法见面时

我会想你的。 
I'll miss you. *miss “想，想念”。
I'll miss you. (我会想你的。)
I'll miss you, too. (我也会想你的。)
I'm gonna miss you. *gonna 是going to...的缩略形式，是比较随便的表达方式。 

我真希望能和你在一起。 
I wish I could go with you.
I wish I could go with you. (我真希望能和你在一起。)来源：考试大
So do I. (我也是。) 

请代我向你的家人问好。 来源：考试大
Please give my regards to your family.
Please give my regards to your family. (请代我向你的家人问好。)
I will. They asked me how you were doing. (我一定带到。我的家人也问过你的情况。) 

你一定回来啊! 来源：考试大
You must come back. 来源：考试大

有空给我打电话。 
Give me a call sometime.
Call me sometime. 

我们什么时候再聚吧。 
Let's get together again sometime.来源：考试大
Thank you. I enjoyed it very much. (谢谢，我真是太高兴了。)
Let's get together again sometime. (我们什么时候再聚吧。) 

请给我写信。 来源：考试大
Please write me (a letter). 

我会给你写信的。
I'll write you (a letter). 

让我们保持联系。 
Let's keep in touch. *keep in touch with... “和……保持联系”、“保持接触”。
Let's keep in touch. (让我们保持联系。)
Will do. (好的。)
Let's keep in touch with each other. *each other “互相”。 

别忘了写信。 
Don't forget to write.
Don't forget to write. (别忘了写信。)
I won't. (忘不了。)