the first thing you need to do is relax.
It could be nothing.
For example, she might be old enough
to be his mother and their 'flirting' is
Of course, maybe this is not true, but
use it as truth for this minute.
REalise that your husband might be
in a pre adultery mode, and get
some adultery insurance...there's
a topic here on that.
Get that first before going any farther.