After Andrew and Cassandra's intimate encounter, they had grown quite close. In fact, Cassandra could now be considered one of Andrew's concubines. Their relationship evolved in a strange way, and ironically, the one who preferred to get closer was Cassandra, who, before having sex with Andrew, was the one who most wanted to distance herself.
At first, she couldn't understand why she longed to get closer to Andrew. She believed it was all due to a temporary infatuation after sex, since she hadn't had sex for a long time, and now that she had, it felt so good that perhaps that was what attracted her.
In short, Cassandra believed she just wanted to enjoy the good carnal sensations for a while after so much abstinence. However, as the days went by, that idea changed. Having a little horniness for a few days after being sexually inactive for so long was normal, but after a cool assessment, seeking Andrew out for sex for several weeks was not normal.