As i mentioned above i think i have the same isue as you. There is no man and after going to mafia the game bugs out. Maybe i need to change the same variable because i dont have a variable for Tyna either. Did you find anything??
I know the variable for the relationship for Tyna from walkthrough. Yes, this is the same problem i go to Nesroth he walks and i get a black screen.
"*BUG ALERT :When you go back to visit Amaria at Point 5 of this section the Quest
variable for Tyna is set to 20. In order to continue it must be set to 17. There is a man
in a blue shirt standing next to Tyna outside of school. If you speak to him and tell him
which Mafia you belong to he will set your quest variable to 17. Do not speak to this
man if you have not completed up to point 5 in Tyna's quest."