Victims of arranged marriage in their young adulthood by their parents, Gaius and Coralista were pretty much indifferent to each other. He had been going steady with his girlfriend Lilith since high school and into university and hoped to marry her, and she was too busy preparing to be the future ruler of Panem to give her romantic life much thought. They surrendered to the marriage and worked out their predicament quite maturely.
They agreed that they would get together to have at least a kid or two for the sake of the succession and make the public appearances etc etc. However in their private lives they agreed to have an open marriage as long as no children came out of their liaisons. Gaius went back to Lilith, and Coralista had numerous affairs over the years. Caligulanus, being a sick man, decided he was going to steal Lilith (who was twice his age) from his father.
After Lilith's death Gaius fell into a deep state of depression and died in less than a year.