You either die a hero, or live long enough to see yourself become a villain

Basically i want a story of a hero slowly changing his views on life and diving more and more into the darker side to achieve his goals.

Basically a anikin skywalker

I guess the obvious two would be Death Note and Code Geass - Hangyaku no Lelouch (although the Code Geass manga is meh compared to the anime).

Here are some others (note that I haven’t read some of these, I just pulled them from similar threads):

Ubel Blatt

A Fairytale for the Demon Lord

Mirai Nikki

Eden - It's an Endless World!

Kimi No Knife

Vampire Juujikai

Anne Freaks

Legend of the Sun Knight

There are tons of other series with the premise you’re looking for, and tons of other threads that have asked for said premise. Try giving the forum search bar a go. It’s at the very bottom of the subforum page. Good luck X)

I don't think Ubel Blatt or Vampire Juujikai qualify. I can't say why for spoiler reasons but I disagree with those choices.