What about God punishing? Does he punish us for fornicating and watching porn?
Punishment is used to get a person to realize they are in the wrong. It isn't used after a person returns to doing what is right. Often God allows the sin to be its own punishment. For example, in a discussion of homosexuality, Paul said, "For this reason God gave them over to degrading passions; for their women exchanged the natural function for that which is unnatural, and in the same way also the men abandoned the natural function of the woman and burned in their desire toward one another, men with men committing indecent acts and receiving in their own persons the due penalty of their error" (Romans 1:26-27).
It is true that some sins have long lasting consequences, not because God is punishing, but because of the nature of the sin. For example, many drugs will impact your thinking for years after you stop abusing the drug. This isn't God's punishment but the physical consequence of the drug (and the reason God said to stay sober).
Fornication can lead to pregnancies, which means you might end up supporting a child for the next 18 to 23 years. You could get an STD and some have no cure. Pornography corrupts a person's view of what sex should be like and changes their attitude toward women. Thinking and attitudes can change with effort.