Ariana Grande confirmed on Twitter that Cat and Robbie will become a couple in a future episode, but this never occurred before the series was cancelled.

What episode does Robbie and cat get together?

In #TheKillerTunaJump, Cat admits she knows Robbie loves her, and Robbie is jealous that she went out with Freddie, also, at the end of the episode, Robbie finally asks Cat out and she accepts, leading to a new relationship in the future.

What is wrong with Robbie in Victorious?

In the episode, Robbie does not understand why he was referred to as a "ventriloquist", which either jokingly indicates that Rex has a mind of his own and is not controlled by Robbie at all or (in a more serious matter) that Robbie suffers from schizophrenia, therefore considering Rex a real person.