"lassen" is very often like "(to) let".
"Let it be" ~ "Lass es zu"
"Let go" ~ "Lass los"
"Verlassen" means leaving, often in the sense of "abandon", somtimes even "dying".
Eg. "Er hat uns verlassen." could mean "Er ist gestorben."
With the same options of misunterstanding like in "He is gone."
Anyway, the simplest translation for your sentence would be
"Morgen müssen wir gehen."