Looking for manga. The main character (gender doesn't matter) has a childhood friend (also gender doesn't matter).
The heroes have grown up and the childhood friend has become an enemy.
However, all the manga I've read on a similar theme are tied to war or enmity between countries/clans/others.
Need a manga where a childhood friend willingly betrays the main character and becomes the enemy, for example:
1) The protagonist was in love with his neighbor, but she fell in love with the protagonist's rival and became an enemy to him.
2) A childhood friend was jealous of the main character's wealth and decided to steal everything from him.
3) The whole friendship was a lie. The childhood friend was just using the main character.
And so on.
I'd be grateful if anyone could recommend me a manga like this.

Alive: Saishuu Shinkateki Shounen
Ares
Berserk although not childhood friends.
And the obvious Naruto but Sasuke is a bitch and I wouldn't recommend it lol

Not sure if these are exactly what you are looking for but thought I would suggest some anyway

[m Mitarai-ke, Enjou suru]
Knew each other as children (though not superclose) betrayal leads to their life situation becoming reversed
[m]Bokura no Koi wa Shi ni Itaru Yamai no You de  
Girl fell in love with a boy. Boy dies and his twin brother blames girl.