It seems Nayanthara is avenging Prabhudeva after severing ties with him. She seems to add up to tension in Prabhudeva. She seems to be experimenting on what would cause irritation to Prabhudeva.
Only Prabhudeva and Nayanthara know reason for severing of ties between each other. Both have not made even a subtle remark regarding severing of ties. Although Nayanthara has severed ties with Prabhudeva she seems to be picking at him. This is the report knowledgeable people give.
It seems Prabhudeva does not like Arya. When in relationship with Nayanthara, Prabhudeva used to pressurize her not to pair up with Arya. Nayanthara has this in mind and seems to have developed much intimacy with Arya.
Also, Nayanthara met Simbu, her former lover, and seems to have spent considerable time with him. They say this is to irritate Prabhudeva.
Thus, Nayanthara seems to be picking at Prabhudeva through such activities. When enquired regarding why she does such things, they say it is a sadistic pleasure she derives from those activities.