What is the ruling of the Sharia and what are the consequences for one who stares for a prolonged period at non-mahram women, and what is the expiation for this sin?

Looking at a friend's wife is haram (definition) (forbidden) because she is a non-mahram (definition). You must repent to Allah, regret this sin, and resolve not to return to it. You should also increase your istighfar (seeking forgiveness) and good deeds. You erred by confessing your sin to your friend; what was incumbent upon you was to conceal yourself, based on the Prophet's (peace and blessings be upon him) saying: "Whoever commits any of these abominations, let him conceal himself with the concealment of Allah."