I am looking for a manga (it's not "level up by eating").
The MC is a young man. He's in love with his childhood friend. She was in the hero's party. When she came back from her adventure, the MC sees her next to the hero and he thinks his friend and the hero are in love (it's a mistake) Well.. he's extremely sad, so, he runs away. He goes to a forest or mountain... He lives there alone... he eats what he can eat to survive... a lot of strange food... he's sick, but each times, he grows stronger and stronger. At some point, he's not a human anymore.
Others things :
- his sister is looking for him
- there is a dragon in the story (later)
It's something I read on a website so it's probably a manga (Japanese translated in English). I don't think it was a manhwa (Korean comic) but maybe I am wrong.