(The Shared Agony spell makes it so that whenever Tyson would take damage, it's split between him and Diana.
The Shrouded Soul spell is hiding Diana's spiritual essence from Arkalas, which is why he hasn't directly gone after her. Tyson hasn't told her this yet.
The Psychic Radar spell lets Tyson know exactly where Diana is)
(How does he diferenciate between her, and the actual psychics?, don't forget there are quite a few telepath in the city)