These can be great experiences providing you are secure within yourselves & you've already worked out some solid ground rules. If you have neither, you can kiss goodbye to a good relationship. And don't think it will make a poor relationship better. It won't do that either.
I was living with Sarah & we were in an open relationship. We decided if one of us found someone to have sex with, the other had to know & totally agree; if they didn't, we were to say no. Also, it would only be a One Night Stand to reduce the chances of getting emotionally involved with this person. It worked really well for us as we were open & trusting of one another & looking back, it was one of the healthiest relationships I've been in. If you haven't experienced it, you may think you understand, though you won't. Sarah & I were together for five yrs & we really loved each another.
Occasionally (roughly every 3-4 months) we fancied having sex with someone else & it was cool; the only weird time for me was the first time. We both decided to find someone on the same night. To give one another space, I went to the Red Lion & Sarah went to the Millers Arms. When I enter my local I find Becky & her friend June. I knew Becky had the hots for me & I also knew it was cool with Sarah so I told Becky about my arrangement with Sarah & suggested she comes back with me that night. She agreed so I was sorted.
A little while later to my surprise Sarah arrives in the Red Lion with a guy called Steve she had found. I knew him vaguely & I was cool about it. Sarah told me that Steve lived on a houseboat & it appeared that they were both going to go there. Maybe it was the alcohol though somewhere confusion set in & Sarah & Steve thought I was going somewhere with Becky. Once we realised this we all decide it would be fine to go back to our two flat which has two bedrooms. We're drinking & chatting in the living room for a while then I suggest that Becky & I go to bed so we say goodbye & disappear.
I can remember Becky spoke posh, had a fantastic body & was highly sexed, though her bum skin wasn't too smooth & she explained this was because she was always riding her horse. Anyway, we're enjoying sex when I hear Sarah & Steve enter the other bedroom which just happens to be right next door & the walls are quite thin. They start getting it on too & I can hear my girlfriend really moaning! That did throw me for a few minutes. I just laid there listening to her with Becky on top of me. It was just a weird feeling. No big deal, just a weird feeling.
Before I started going out with Sarah, I had a lover called Paula. Not a girlfriend, a friend who I would occasionally have sex with. Occasionally I would sleep with Paula while I was with Sarah & Sarah was cool about this. The three of us used to go out drinking & clubbing together too. I don't know which of us suggested it though one of us came up with the idea of being talent scouts for each other. If one of the girls spotted a girl they thought I might be interested in, then would check with me & if I was, they would tell the girl & then bring her over to me. Great! I didn't even have to bother looking for any girls! I did the same for them. Nice arrangement!