The theater was overcrowded.
over= super; crowded= lotado,cheio

I'm happy with my girlfriend but unhappy with my mother.
Prefixo un= des
happy= contente

So much can agree to disagree depends on the circumstances.
Agre:Concordar
Disagree:Discordar
Dis= Não

This work was perfect but the other was imperfect.
Prefixo Im+ perfect= Imperfect

It is impossible to leave, to like you.
im+ possible= impossible
im+ possível= impossível

In childhood I was very mistreated.
Mis= Mal Treated=Tratado.

Misbehaviour hinders learning.
Mis= Mal Behaviour=comportamento.

I will remake all my exercises.
Re+make= remake.
Re+ fazer= Refazer

I'll tie this rope and then go untie.
TIE= AMARRAR
UNTIE=DESAMARRAR
PREFIXO UN=Não

It was unfair to his employee ..
Un= oposto/Não
Un= Não Fair= justo
Injusto