(idiom) keep in touch, let’s keep in contact even though we’re parting
I’m going back to Brazil and you’re going back to Italy. Here is my e-mail address, please don’t be a stranger!
Student 1: I am going back to Brazil.
Student 2: I am going back to Korea.
Student 1: Good luck to you! I hope we will meet again soon!
Student 2: Don’t be a stranger!
Have fun on your vacation! I hope you enjoy Mexico! Don’t be a stranger!