Both of them in my case. I've several experience between my wife and her black friend.
Perhaps in my case is a little diferent due I know our black friend Axel because we worked together.
During our second encounter, Axel was lying on our bed and Susie sat over his cock to fuck. One or two minutes later, she had her first orgasm. Axel kept fucking for 20 minutes more, until he said that he was trying to cum. When Susie took in count he was close to cum, she begged me to suck her nipples, due she wished cum together. I sucked her boobys while Axel continued fucking her, until they finally found their own orgasms. It was a real honour for me assit her during the fuck.
I only participate if invited. I actually prefer watching to participation. I feel the other man or men are there to participate. When my wife asks or the men ask me to, I will join in.
I am bi. So, I do like to get involved where I can be the second woman in the action.