It is open to different interpretations but this is my take on the phrase.
"절정" is also used when someone or something is in their/its prime. So the phrase means "Everything that has passed its prime, many things that wither by losing their youth after all"
The next phrase means
"I wonder if you realized that my heart is going to hurt a little, heal slowly, and forget (what happened)."
Your Korean is good! =]
I hope this helped.