It's exactly what it says, on one hand, saying that people must learn to voice their concerns and problems or else they will never be fixed or noticed.
On the other hand, you could take a much deeper look at it and show how people ignore each other's pain often when it is not plainly voiced.
It probably depends a bit more on context, but this should be good enough.
It means that if you do not speak up about being depressed or "in pain" people around you that you interact with will unknowingly kill you on the inside and when/if you speak up they will assume you enjoyed it because you did not speak up before. Its a metaphor you see... if someone were to continuously stab you and you didnt speak up, they would stab you to death and assume you liked it for not acknowleding your pain. (excuse my terrible grammar im using an uncomfortable tablet with no auto correct and am trying to type this fast.)
The type of sentence given is a compound sentence. It is a compound sentence because it consists of two independent sentences: "I already said yes to someone else" and "I can't go to the dance with you". In order to link the two sentences, the conjunction "because" is used.
An officer (police officer) is someone who fights against crime, and helps prevent it from happening. A criminal starts crime, and causes trouble for the police officers.
