[funrealcouple]

As with husband and wife, if one is uncomfortable, the other should back them and they should talk it over.
If she goes out without your blessing, she is cheating.
The same as would be if you were going out. Male or female it does not matter.
If I were you I would sit her down very nicely, not offensively, and tell her how you feel and that if she is choosing the lifestyle over you then you will be gone.
It all has to be calm and non-threatening.
You 2 need to talk.
Like the quip, "It's all fun and games till someone loses an eye" or in your case
I would say "get's their heart broken".

I'm afraid she is already lost.
Good luck.

FRC