Happy to see you again...,

[Silverobama]

David is a friend of mine. He went to the UK to study five years ago. I saw him last night and I was a bit surprised because he didn’t tell me he’s back.

Silver: David! When did you come back?

David: Hey Silver. A couple of days ago.

Silver: Happy to see you again! How long will you stay in Chongqing? Are you going back to the UK?

Is the italic sentence natural?

 

[emsr2d2]

David is a friend of mine. He went to the UK to study five years ago. I saw him last night and I was a bit surprised because he didn’t tell me he’s he was back.

Silver: David! When did you come get back?
David: Hey Silver. A couple of days ago.
Silver: I'm [really] happy to see you again! How long will you stay in Chongqing are you back/here for? Are you going back to the UK?

Is Are the italic sentences natural?

See above.

When two people are in the same place, and you're referring to that place, it's quite unnatural to keep referring to it by its name. You do that a lot!

 

[Rover_KE]

There are three italic sentences.

 

[teechar]

Also..

Are you going back to the UK after that?