Your fundamental personality traits are going to exist in or out of a relationship. Your values, tendencies towards altruism, selfishness, kindness, cruelty, willingness to try new things, introvert, extrovert… Those tendencies won’t change but a relationship is going to cause those tendencies to manifest in different ways.
To use an overly simplistic example of someone who is shy and introverted. Maybe the confidence and security of being in a couple makes you less shy and so you go out more. Maybe it means you stay in more because it makes staying in ‘acceptable’. It probably depends partly on the other person and their own personality. The inherent shyness isn’t going to go away but the relationship will bring it out or dampen it in some way.