This depends on the context of the phrase.
If you want to only say "before we leave"
If there is another clause after "before we leave," like "Before we leave, I want to eat,"
This also works for a phrase proceeding "before we leave," like "I want to eat before we leave."
Alternatively, the phrase "before leaving" can carry the same effect, and Antes de salir can be used with a proceeding or succeeding clause.
Antes de salimos...
Ahn-tehs deh sall-ee-mos
i want to see you tonight and spend time with you before i leave
antes de dejarte ir quiero decir que te amo
There are several ways to tell someone to leave in Spanish. One can say dejar. Another way is to say salir. Yet a third way is to say abandonar.
licencia entoces
Voy a irme
Alístate para ir.
nunca me dejes
No salgas -or- no te vayas
I would just leave it as "Dexter".
Baby don't leave = Bebe no te vallas
salir de la casa
Hola, dejame mensaje.