What is the ruling on habitually looking at and touching the 'awrah between two young men, and what is the expiation for this act?

Your friend committed a grave error by looking at your private parts, and you also erred by retaliating in kind. While retribution in kind is permissible in Islamic law, as stated in the Quran: "So whoever commits aggression against you, aggress against him in like measure as he aggressed against you," and "And if you punish [an aggressor], then punish with the like of that with which you were punished." However, this restriction does not apply to forbidden acts such as adultery, sodomy, or looking at private parts. Retribution in kind is not permissible in these matters. Touching another person's private parts is forbidden, unless the one being touched is a child under seven years old; in such a case, there is no harm, provided there is no temptation. Al-Bahuti said: "It is not forbidden to look at the private parts of a child before the age of seven, nor to touch them, according to the text, and it is not obligatory to cover them, meaning the private parts of a male or female child (provided there is no lust)." I thank Allah for your repentance and seeking forgiveness.