I am in an open relationship as such, I dominate men but never anything sexual. However I am sexual with other women.
My partner and I talk a lot and are very open about our sexual tastes and desires, he is fine with me having relationships with women as I am open about it, it is not cheating if everyone involved is aware and fine with it. If I went behind is back it would be.
If he was sexually interested in men, then I would be happy for him to try things, if I was there or not, as long as he was open with me.
However, I do not or would not have a sexual relationship with another women or a man simply because my partner asked me to. Same as I wouldn't expect my partner to.
The unfortunate fact about many men is that they are willing to share their girlfriend with another woman and want to get involved (threesome) but are not happy about it the other way around.
If everyone involved is happy and aware of what is going to happen then I would say try it. Be aware that for many, the harsh reality of sharing partners leads to jealousy, arguments and often break ups. My suggestion would be never go with anyone you are friends with, not worth the friendship and or akward times. The best option for a one off is a paid sex worker, then you will never have to see them again.