Translation: Estoy triste cuando no estoy contigo.
You could also say "Me entristezco cuando no estoy contigo" (I sadden when I am not with you), but this is more literary, although the emotion comes off more strongly.
Just as a note to your translation: "con tú" does not exist in Spanish and always becomes "contigo". (The same with "con mí" becoming "conmigo". "Consigo" has a set of unique rules which is why "con él", "con ella", and "con Ud." do not automatically become "consigo".)
when i am sad : cuando estoy triste.i am sad : estoy triste.
It means, I'm still sad ,when my mom hit me with a helmet.
estoy triste
Estoy feliz cuando estoy contigo.
Siento tristeza Estoy triste. Me siento triste.
Estoy triste.
cuando estoy...
"Cuando estoy contigo" means "when I am with you" in Spanish. It is used to express being together with someone.
estoy molesto (for guys) molesta (for girls) contigo
Estoy triste (I am sad right now) Soy triste (I am a sad person)
English Word: sadSpanish Word: triste, afligido
If you mean 'When I arrive' - Cuando llegare If you mean 'When I'm in that place' - Cuando estoy alli.