Regarding lesbianism in Rokugan:
L5R has one open homosexual and one very blatant closet case in the canon NPC's. Both of them are male. Ignoring the matter beyond that is intentional as the game must still be marketed to "the masses" and homophobes spend money, too. It exists, and the above posters that reference "discretion" are spot on.
Adultery is actually extremely common in Rokugan on both ends of the spectrum. Husbands that spend great lengths of time away from home will find someone to spend their idle hours with, frequently in highly sexual manners. Wives whose husbands spend great lengths of time away from home will do the same.
- No Children = No problem
- Husband has illegitimate children = Ignore them, Quietly pay mistress for care, have them killed, or mysteriously adopt child into household while giving some bullshit story about how it is to repay an obligation.
- Wife has illegitimate children = Lie about it. Now they are legitimate.
Case in point: Bayushi Dairu. He was the illegitimate son of Bayushi Kachiko and Doji Hoturi. Bayushi Kachiko's husband, Bayushi Shoju (then Champion of the Scorpion) knew that Dairu was not his, knew who fathered him, and never said a word about it to anyone, including the wife that bore him. Shoju not only treated Dairu like a trueborn legitimate son in public, but adored him like his own flesh and blood.
Exception: The Spider punish Adultery with death.
Regarding Rokugan and Politely Ignoring: Based on Japan, where if a billionaire businessman farts in an important meeting, it doesn't matter unless someone giggles -- Then it causes a tremendous loss of face. Rokugani are very good at "looking the other way" when things happen that might embarrass someone, and infidelity is one of those matters unless their are underlying motivations otherwise (spouse is family, blackmail urges, problematic lack of subtlety, etc.).