Complex sentence: But after an astrologer told her uncle that he or his niece would die soon, he decided to marry Rasathi, thus making her his wife and getting her wealth, reason why she had tried to commit suicide earlier and is now running away from him.
Split into simpler sentences: But after an astrologer told her uncle that he or his niece would die soon, he decided to marry Rasathi, thus making her his wife and also to get her wealth. That was the reason why she had tried to commit suicide earlier and is now running away from him.