Love and Marriage

Marriage:

Marriage in Rokugan is generally a political affair. It is often used to seal treaties, where a member of each side will join the family of the other side. The idea is that if a Lord marries their child into the other side, they are less likely to attack, especially when they have grandchildren born there. The individual moving to the new side is expected to obey their new Lord and their spouse, but also to act as an advocate for their old family.
The marriage negotiations usually determine who will take the name of their new spouse. The first determinate is status: usually, the lower status spouse takes the name of the higher status spouse. Exceptions can be made as a punishment. The marriage can be a way to demote a samurai, especially if they have underperformed or embarressed their clan. They are sent to the new family as a punishment.
For most families, where possible, they want sons to keep the family name, and expect daughters to change it. This is not universal however: sometimes an incredibly talented daughter will be groomed to be heir, and her brothers instead will be marriage fodder. Gender is one of the last determinates, after status and ability.
There are two Families that almost never marry their daughters out, except as a form of punishment. The Lion Clan Matsu Family and the Unicorn Clan Utaku family are both matriachal. They expect sons to be sent to them, and they send sons to other families.
The majority of marriages are within Clans. A lot are within distant branches of the same Famliies (as a Rokugani Family name is shared by 1000s of Samuria.) Next one will find marriages amongst Families witin a Clan. Finally, there are interclan marriages. These happen more often with samurai who live near the borders of other clans. However, any treaty between clan can include a number of marriages to strengthen ties. Usually, there is an equal exchange: one samurai leaves the clan, and another joins, but this is not required. Depending on the treaty, this could be extremely lopside, and there may be no entrances into one clan.
Marriages are expected to be herditary, and couples are expected to produce at least a single heir. Because a couple can be married as part of a peace treaty, there is a strong possiblity of eneminity between spouses. Spouses are expected to follow tennants of bushido, and act with respect, courtesy, and honour towards each other, but it is not uncommon for spouses to dislike each other, and only appear together when their duties demand it.

Love

Love is considered related to, but seperate from marriage.  It is considered an important aspect of life, and one of the Seven Great Fortunes is Benten , the fortune of Romantic Love.  Samurai are likely to fall in love, but it is considered rare and blessed that it happens with one's spouse, to the point where a Blissful Bethrothal is a mechanical advantage within the game.
Since samurai fall in love, but not with their spouses, romantic relationships and even affairs are considered somewhat normal in Rokugan.  The important thing is to conduct such affairs in a way that would not dishonour one's spouse.  Discrete affairs are considered to be normal, but are to be kept private, and not flouted in public.  There is nothing wrong with having an affair.  There is a problem with being caught having an affair.
This extends into an interesting tradition at many Winter Courts.  A samurai in the admidst of an affair will leave poetry to be found, declaring the depths of their love.  The intent is that the person their speaking to will know who sent it, and that it is for them, but no one else will know.  It is the height of a courtier's skill to publically declare their love, be the talk of court, and never be identified as one of the lovers.
Because a geisha technically belongs to the Eta class, there is no issue in spending romantic energies on them, as long as it does not interfer with any aspect of a samurai's life.  The expectation is they will also keep these engagements discrete, and not flaunt them.  However, to see a samurai entering or leaving a geisha house is not considered to be scandalous in any way.
Culturally, tales of forbidden love are considered high art.  Tragedies, where a samurai must sacrifice their love for the sake of honour, or vilinaous tales where desire leads a samurai astray, are ever present in theatre, poetry, and especially pillow books.  In high art, love is always an obstacle for honour, and the lesson is always to chose honour or face the consquences.  Lower art may question these priorities.