Complex sentence: Occasionally, she shows signs of possessiveness towards Sebastian and the two of them are in love with each other, though they share a complex relationship; as Kathryn puts it that they're "two of a kind".
Split into simpler sentences: Occasionally, she shows signs of possessiveness towards Sebastian, and it is suggested that the two of them are in love with each other. They share a complex relationship; as Kathryn puts it, they are "two of a kind".