Reading the summary on Nova Vassa, if I were to redo Tristan, this would have been my take:
Tristan's father, Romir (a Hiregaard) and mother, Kavela (a Vistin) were bound together in an arranged marriage that was meant to give the two houses enough combined power to eventually seize power permanently from the other families). It was a marraige with little love, though it born them a single heir - Tristan.
Romir, however, was too caught up in duty and shoring up the two families to have much to do with his family. In many ways, the father had been placed under great duress to present a face of strength and dignity internally to the family and an air of aloofness towards the other families to belie the two family's growing power - especially that of the Hiregaard. Internally, this created a black heart of jealosy in Romir, especially towards thing he deemed as rightfully "his". Likewise, Tristan's father drilled his own sense of duty into his own son.
Tristan's mother was a much freer spirit, and though she was not allowed to dote on the youth, had much more latitude to interact with him and guide his hand in matters away from the affair of state. She was, in many ways, his conscience. However, as Tristen grew up, Kavela's despair at the lack of love between her and their father wore deeper and deeper. Then, one day, everything changed.
As royal functionaries, it was the duty of Tristen's father and mother to attend and host various functions - among them, dances for the nobility. A new dance had recently made its way through the nobility and with the approval of Romir, the young boy's mother hired a bardic instructor to teach them the new dances. She did not expect, however, to become attracted to the rakish bard, all under the watching eyes of her son.
One day, young Tristen was with his father when the elder asked how the dance lessons were proceeding. Tristen answered truthfully - a little too positively and eagerly that intrigued Romir to visit and see for himself. Arriving unannounced, he observed teacher and student in an intimate dance upon the ballroom floor and observed in secret and silence, all as he fumed in rage. Tristen watched from beside his father, fear gathering on his face as he watched his father's expression fall away to hate.
As the young rake was departing, Romir emerged from his hiding place. With a single sweep of his blade, he cut down the bard without a word. He moved to his wife and grasping her, accused her of infidelity. Tristen, shocked and unmoving, could only watch. At first, his mother pleaded with his father, insisting no wrong had been done. But Tristen's father would hear none of her words. As he pronounced his judgement upon her, her pleading ceased and the years of regret and despair she had endured sprang to the fore. She did not spare her growing anger as the two bickered, but she placed the burden of raising Tristen alone on Tristen's father as well. Enraged beyond all reason now, hurt by his own mother's words against not only his father but himself, Tristen leapt from his hiding space, tears smearing his face and he bodily rammed his father's blade into his own mother. As his mother, collapsed, shocked at her son's own betrayal, she cursed them both. The power the family had craved would never be realized, and she furthered cursed that her murderer to never enjoy love - murdering it as she had been murdered.
Tristen, coming to his senses, was deeply shaken by his act. But his father remained stern, convinced Kavela had brought her own death upon her by her faithlessness. Tristen had no choice but to agree. Tristen's father covered up the death, twisting it to use as propaganda against the other houses to sow fear and suspicion that the other families had been behind the plot.
A handful of years passed, and Tristen's father continued to immerse himself into the politics of the houses. However, his attempts to consolidate power began to alienate the Visten family, who began to chafe at his callousness towards their deceased heiress. The other families treated Tristen's father as "unlucky" and his attempts to woo them only drove them away and towards the rising Bolshnik family.
When Tristen was sixteen, a young scullery maid in his household, named Ivanava, caught his eye. Under his father's tuteage, the young man was not hesitant to approach her, though he did do in secret to avoid any appearance of impropriety. This continued for several months in absolute secrecy, until Tristen began to suspect that Ivanava was speaking of the courtship to others in her family. Tristen then lured Ivanava to a secluded area of the keep and murdered her with a blade through her heart. However, after he done so, he felt great remorse and confessed his act to his father. Though his father was stern and rebuked him for his weakness for love, he covered up the murder, making it appear the young lady had fallen from the tower accidentally.
Shortly thereafter, Ivanava was replaced with the young woman's twin sister, Vivianista. When she made a remark after meeting Tristen that her sister had been right about how handsome he was, Tristen's blood ran cold. Afterward, Tristen made attempts to find out how much Vivianista knew about his former love for Ivanava, and as he associated with Vivianista more and more, he inadvertently fell in love with her. However, their love was doomed - Tristen eventually confessed his deeds, which horrified Vivianista. She fled the castle from him, and again Tristen turned to his father and admitted his latest mistake.
Romir flew into a great rage, and ordered Tristen track down the girl and ensure her silence. Tristen obeyed, and rode out alone in search of Vivianista. His trek lasted several weeks as he followed the fleeing girl's trail. In several cases, he found himself forced to kill someone who he suspected had sheltered the girl or who he believe she had confided his dark secret with. Eventually on the night of a waning moon, Tristen tracked her down to a barn on the edge of Vaasa's lands. He found her inside, hiding - and she begged Tristen for the love they shared that he spare her. Citing his duty, Tristen refused to requite his love and struck her down. Afterward, he burned down the house of the accompanying farm and slew its fleeing occupants before the dawn broke, ensuring he left no witnesses.
Tristen returned to his father under the cover a thick night's mist, with bloody proof of his deed. Romir, however, was not pleased at his son's performance and berated him liberally for allowing his foolish desires to interfere with his duties. Thoroughly chastised, Tristen agreed, "If I am not to have love, then I will have duty!" - and ran his father through. As Romir faded, he bemoaned, "what monster have I created?" and the mists outside the family castle thickened and engulfed him.
Tristen awoke to a changed realm, and after concealing his father's murder, took to his new duty as lord of the Hiregaard lands. But once a month, on the night that matches the moon above the barn where he found Vivianista, he transforms into a hideous monster, bent on slaying those he had once cared for, among his own household and the surrounding lands.
