<human>: Can you give me a shortened version of the text?

Myself and my girlfriend have been together for 4 years and we have generally had a good relationship. She has had some mental health issues (anxiety and depression) but we have worked through them together.

She recently approached me saying that she wanted a dom/sub relationship outside of our relationship (At the same time as dating me). I did not like this as I value the intimacy of just two people together with no other people involved. I also believe that sex and sexy time is something that should be exclusive to the one person you are dating.

I'm wondering what everyone's thoughts are on this / how we can try deal with this within the relationship? As i really dont want another person as a part of the mix.
<bot>: Girlfriend wants dom/sub relationship but im against it. What can we do to resolve this without involving someone else?