- (Optional) Revealer: something/someone that reveals the crime, betraying the trust of either the Lover or the Beloved
The crime is related to Lover and Beloved's relationship, most often infidelity in some form.
This is a story in which PCs may be distributed between the Elements, with a few as kinship of Lover, others as kinship of Beloved (or common kinship) even one of them as Revealer.
Is the Element that makes the error against its relationship with Beloved.
PCs as Lover
Not every PC would be the actual Lover, and often none of them will, but they can be the actual Lover's friends or family.
It is the person betrayed by Lover's crime.
PCs as Beloved
Again, the PCs may and probably will be the actual Beloved's friends or family.
Revealer may be because of jealousy. If Revealer is in love with Lover or Beloved it can reveal the crime to end the relationship and have its own chance.
Revealer may be common kinship of both Lover and Beloved, such as Lover's brother and Beloved's friend, and doubt between the loyalty to both, finally folding to the innocent Beloved and revealing the crime.
Revealer can do so without good intentions to anyone, just to take revenge upon either or both Lover and Beloved.
PCs as Revealer
As in other cases, this is something you can at most give the chance for, because you don't know what the PCs are going to do. Just take two NPCs of your campaign with good relationship to most or all PCs, introduce their own relationship slowly, like background story, and have them announce the PCs their will to get married and committed to one another.
Then, not too much time before the wedding, have a few PCs learn about the crime. If they learn about it in different ways - maybe one of them is witness, other is trusted by Lover with the story, etc - it can add an inner intrigue layer since each one that knows the secret may want to be the only one.
Do the PCs reveal the crime to protect the Beloved? Don't, to protect the Lover? Decide to forgive the Lover's crime and not to tell?
The crime itself may be a Conspiracy or a Fatal Imprudence.
When the crime is revealed, from the betrayed spouse it could be Discovery of Dishonor in a Loved One, provoke him Madness, and/or develop in Pursuit or Vengeance.
The Betrayed Spouse may also Sacrifice the relationship it had, his good name, etc leaving the adulterers be.
A divorce may be considered a Disaster from the left spouse. The very adultery may be a Disaster from the Betrayed Spouse perspective.
The crime may easily mix with or be the result of Rivalry