She's giving him some major "buy" signals. Does she realize this? I would point it out to her. Act concerned that he may take some action based on her behavior.
You can be a bit of an alpha male here. Women like a LITTLE chest pounding. Just be loving AND say you don't like that kind of shyt. She is YOUR woman.
It may have been completely innocent, but at least you've let her know what your boundaries are....(but, we women usually know what we are doing!

)
If it continues, I would pull back a bit and say that while YOU love her, she seems confused about wanting to be with just you.
That might open up an important discussion about your relationship and if and how you can meet each other's needs.