Looking for that one Manga/Manhwa about a psychotic guy...

It was about a boy who loved his adoptive brother so much that he'd kill anyone who will come between them. He has some issues and he knows that, but he doesn't know how to deal with them.
It's also about the brother, who knew something was wrong with the boy, but didn't do anything out of selfish reasons.

The whole thing starts with something like "Yes, I have killed them. I will tell only you since you look like my brother and not like a disturbing monster. This is the story why I killed innocent people."

I think it was finished like a year ago, but I can't figure out how it was called. I'm pretty sure the title was english...