Answer:
The Picture of Dorian Grey by Oscar Wilde
Step-by-step explanation:
Its about a handsome young man who trades his purity for his beauty. It all starts with an artist painting a portrait of Dorian that perfectly captured his beauty and countenance. When Dorian sees it, he realizes that he won't be young and beautiful forever so he wishes that the painting would age instead of him. Lo and behold, that exact thing happened and Dorian is basically immortal. However, to cover up his unnatural state of being, he must do things that betray his innocence and purity. Dorian becomes an evil man while his painting ages and rots away. I won't say anymore because I want you to read it :)
If you like books that explore the dark side of human nature, then this is a great book for you.