to move in together, to shack up
Eu acho que deveríamos juntar nossas escovas de dentes!
I think we should move in together!
This is a modern, playful colloquialism rather than a historical phrase. Juntar as escovas de dentes literally means "to put the toothbrushes together," and it pictures the small but telling moment when a couple's most personal daily objects end up sharing the same bathroom cup.
Falando's Idiom Trainer teaches you to recognize idiom meanings and create sentences using them, so you can speak like a Brazilian.