Learn English – Single word for “more than once”

Multiplex as a word has been around for centuries. It was not invented for cinemas.

As for the opposite, it seems to be uniplex - and uniplex, and uniplex.

Ngram shows 'uniplex' suddenly appearing in the 1970's, though it is only fair to point out that OED doesn't list the word.

[…] the feeling of say, getting a happy ending at the end of a tragic movie--like 'glad', but stronger.

This feeling is called catharsis.

I don't think there's a word that fits into the same syntactic slot as glad, though. (There exists an adjective cathartic, but it's used to describe the experience — the thing that causes or triggers the catharsis — rather than the person.)