If we have a typical winter you could lose your Butterfly bush if you cut it back now. In the north it is best to wait until spring.

I took care of the drooping problem with my bush by putting a very sturdy tomato cage over it in spring when I cut it back. I removed any errant lower stems and now it grows up through the cage and stays much more upright. The one on the side of the house I didn't do that so I have to remove a lot of the lower stems as they start extending out into the yard.