First of all, I feel you with not wanting to be pushed into a friendship with the GF until ready. I have hurt my metamour's feelings in the past by not being as close to her as she thought we were (or wanted us to be) and all the pushing does is push me back, not forward. It might be best to make sure your hubby knows that the pushing will continue to backfire, and it'd be best to leave things up to you and the GF.
Second of all, my perspective as an endpoint of a "V" is that, if my metamour wanted to know every single detail of my sex life with my partner, I would have a talk with her, as soon as possible, and tell her that I am in no way comfortable with that (and if that were unacceptable, I would no longer be intimate with my partner, and would quite possibly end the relationship). I would honestly feel violated if my intimate moments with my partner, where I am at my most vulnerable, were shared outside of the two of us.
Remember that it's not just your hubby's privacy; it's hers too.