I remember how hard it was to be Mr. Bad Guy and to be the one to take that first step towards separation. I kept thinking a giant cartoon boulder would fall on my head for even saying the words "I want a divorce". In the end, HP arranged it so my XAH was the one to start the dreaded conversation, but there were a few instances afterwards where I had to squeak out "No, I don't want to be with you anymore", and it was so difficult. Once I did it though, I felt...liberated.
Perhaps the issue of your departure just isn't up for discussion with your AH. Perhaps you will just line things up and leap...and tell him later.