Catherine is the love of Vincent's life. After saving her life he watched over her for many years to make sure she was safe, which also helped him hold on to a piece of his humanity. When Vincent revealed his secret to Catherine, she looked past his physical changes, and saw him as a man and not the beast he became after the experiment. Catherine told Vincent that though he was no longer human, he wasn't a monster, and she believed that he was more human than he believed himself.
After learning that her mother was a part of the team that turned him into a beast and falling in love with him, Catherine's life soon centered on protecting Vincent from people trying to use his abilities, as well as doing whatever it took to hold onto their love.
Vincent initially sought to push Catherine away, Catherine refused to leave, and he became able to accept who he was because of their love, seeing his change as a gift rather than a curse. When Vincent chooses to be more beast than man, his decision ends their relationship. After their break-up, Vincent's dark side is shown, consumed by violence and rage, acting ruthlessly. He eventually realizes his mistake of letting his beast side take control and resolves to redeem himself for Catherine.
After changing so much that Catherine could not recognize him, Catherine pushes him away, but Vincent doesn't give up and fights to prove himself to be the person she once loves. After proving to Catherine, that he can be more human than a beast, they resume their relationship. Catherine puts her entire life at risk to protect Vincent's secret for the sake of their love. Vincent told Catherine that he could control his beast side only because of her and the love they share. Vincent saved Catherine's life, but Catherine saved Vincent's humanity. This TV couple has been through so much yet their love makes them a perfect team, and they learned over and over that together they are invincible. Which is why Vincent & Cat are Sueboohs Corner 2017 Countdown to Valentine days #8 TV Couple of 2016.
Here is a video from some of Vincent’s most and Cat’s precious moments.