If your significant other asks to start sharing and swapping with other people, i think you have to do it. Me and my bf have been doing it for years now and i love it. Most of the time its both of us having a threesome with another girl but sometimes he invites his friends over and they all share me. Sometimes im just bent over the couch and sometimes i just lay on the bed with my legs spread and they just take turns. My favorite though is watching him cum in another woman while her bf or husband fucks me. He likes to choke them and call them cum sluts and theres just something really hot about watching that.