Wow...good luck with your meeting with her!!
Has he exhibited any of the "white night" behavior before in the 8 years you've been together? Sounds like "rescuer" behavior.
In your explantion of the situation, I can see that the most common triangle pattern is:
the reason you have to become the perpetrator is because that's how the triangle works.
Then- when you put your foot down it shifted to:
Now- with you going to talk to her, there is a possible inevitable shift of:
Anyone caught in this type of triangle might want to do some reading about it. There is a pretty good simple book called The Power of Ted and it takes a new spin on the Victim,Rescuer,Perpetrator triangle phenomenon.....transorming them into Creator,Coach,Challenger respectively.
Again- good luck!
The key to life is in being fully engaged and peacefully detached simultaneously and authentically in each moment.