What did Fredo Corleone actually do?

[KennyBanya]

Hi,

I was watching The Godfather Part II last night for like the 10th time. There is a part of the storyline I dont fully understand.

What is it Fredo actually does to betray the Corleone family. I know he lies to Mike about never having met Johnny Ola, and then Mike catches Fredo talking about Ola later.

Is that it? My only other guess is that Fredo opens the curtains in Mike's bedroom so Hyman Roth's assasins can try to kill Mike?

Maybe the novels explain Fredo's bertayal better?

Please help this slow on the uptake Godfather fan.

Peace,

KennyBanya