Pornography and masturbation represent the destruction of the symbolic and nuptial meaning of the human body.
Sex does not belong only to the physical world. Rather, sex belongs to the world of symbol and the world of love.
Do husband and wife have to intend having a baby every time they have sex? No, they need only reverence the sexual act and remain open to each other and to the possibility of a new life.
Contraception is any act done either before sex, during sex, or after sex that is intended to prevent the conception of a new life. The Church has always taught that contraception is wrong, but it has used different reasons over time.
A divorce is said to end a valid marriage, but a declaration of a annulment says there was no valid marriage in the first place.