I would end the relationship. I'm not the kinda guy who has tons of kills so it would really get to me.
Soft as butter...lol
I have had serious relationships with a couple different woman that wanted to do a 3 way with her , me and another dude.
One wanted to go to sex swinger clubs as well.
I have no moral hang ups against it, BUT, I am not comfortable with that kind of activity , so the relationship ended each time.
For me sex is one man and one woman without toys or devices.
Once again , to each his own. BUT, I like good basic sex with a lot of positions, period