Finding the boar is what triggers the bite night. If you avoid it you should be able to postpone the reveal for quite a while. (Going to the Underdark or the Mountain Pass will also trigger his confession about his vampiric nature, so avoid those too)
In my case, during my first and second run, I had the biting scene before finding the boar. 1st run under patch 5 and 2nd under patch 6
