This experience happened to me a few years ago and it ended up being a couple that I got to 'join' about once a month over a six-month period. They were pretty hardcore swingers and I think I learnt some good skills (particularly from the husband on pleasuring women).
This is what I wrote at the time just after the first time we met.
Last Friday night I had a threesome with a couple that I met online. A friend of mine recommended this couple as good fun. I spoke to them online before I arrived here and they seemed really keen and also rather experienced.
Friday night came along; I met them at a bar in town after dinner. Lots of photos were exchanged beforehand and they looked like their photos. I told them I was bi and they said that the husband was 'open-minded'. After just one drink, we were getting along fine and the wife asked if maybe we should head back to their place for another drink. It sounded good to me as I was getting a hard-on in my jeans and black speedo already.
Their house was only a five-minute walk from the bar.
When we walked in, the husband went to the kitchen to make some drinks and the wife pushed me down onto the couch and we started making out. Our lips (and tongues) were locked until the husband came back with our drinks.
At this point, the husband sat on the couch next to me and his wife got off my lap.
"Well, Dave – you told us that you like bikinis and speedos. How about you guys get down to your speedos and I’ll go put on a bikini…"
While the wife left, the husband and I did what we were told; we stripped down and it turns out we were both wearing a black speedo under our jeans (I had told them I'd be wearing speedos under my jeans beforehand).
I was hard as a rock from making out with the wife and the husband was slowly getting there. It was pretty hot sitting on the couch next to a married guy, both in speedos, rubbing our cocks through the lycra waiting for his wife to join us.
So the husband and I were sitting on the couch, both wearing black speedos. I was hard as a rock from making out with the wife and we were both sitting there rubbing our cocks through our speedos. It didn't take long until the wife returned. All she was wearing was a white bikini. She is petite, nice medium-sized titties, shaved all over and brunette.
She noticed straight away that I was harder than her husband, and getting on her knees between his legs, started rubbing the front of his speedo. First, with her hands, then with her mouth.
After watching this amazingly hot sight, I decided that I should look after the wife. I needed to cool down a little bit as well. I got off the couch, and lying on my back on the ground, I put my head between her legs, pulled her bikini aside and tasted her moist pussy. My attention to the wife's pussy was met with a groan of pleasure from the wife, and she started to grind her pussy on my face. I assumed the husband's cock was free of his speedo and his wife was sucking hard on it.
After a little while, husband told me that I could fuck his wife from behind if I wanted to. I was still super horny but I had cooled down a little bit and thought that I wouldn't blow my load after two strokes, so I grabbed a condom and got on my knees behind the wife. Sure enough, husband's speedo was pulled down and wife was sucking away on his now very hard cock. Wife's pussy was well and truly wet from the attention my tongue had given it over the previous five minutes, and my cock slid in easily and the groaning coming from wife's cock-filled mouth with every thrust of my cock indicated that she was enjoying having a cock in both ends.
Both husband and I were starting to get really hot and I knew I was keen to hold off for a little while.
Thankfully, husband had the same idea and suggested that we move upstairs into the bedroom.
So the three of us put our genitals back into our swimwear, took a deep breath and moved upstairs...
Round two saw us move from the couch to the bed. The three of us were chatting casually; the wife was between husband and myself and all six of our hands were slowly exploring each other.