"He's gone" . . . Do you mean something like "He already left?" In my experience, they use "Ya se fue" here, which basically means "he left already, he's gone". That's probably what you want.
"When will you be back?" - "Cuando va a volver?" (Since I assume you want the polite form, this being a girl talking to an adult she doesn't know that well.)
"You were sad." - "Estaba triste."
"You're still sad." - "Todavía está triste."
"You love him." - "Usted lo ama."
"I promise." - "Lo prometo."
If I'm wrong, someone correct me here. Anna's caught a few mistakes of mine before . . .
