The English language allows for several variations on the majority of sentences, in this case you could say "nice to meet you again." Stating that yes it is nice to meet you but that you have met before. I haven't seen you in a long time, I'm happy to see you again, it's been a while, are all usable; there's many options. The key to English is to be able to rephrase multiple sentences and still keep the original meaning.

Long time no see.

in this case you can also use, " it's a pleasure to see you again"

Long time no see is used as greeting(Origin: in humorous imitation of broken English spoken by an American Indian)=It's a long time since we last met.

Yes you can use it. You can say it like this: "Nice to meet you after such a long time."