Fan Casting Commitment Issues in Sort by Tropes

A character with commitment issues does not want to settle down with a Love Interest. They may think that being married is inherently boring and unadventurous, or they believe they're still not old enough to be serious yet, or they have issues stemming from observing the dysfunctional relationship their parents had, or being a swinger is just too much fun, or maybe they're Really 700 Years Old and are afraid that by committing they'll outlive the person they love.