Happened a couple of months ago and finally decided to share.
My wife and I were just chilling at the hotel bar after dinner and a long day. We were hanging out by ourselves, and after a few drinks, an older man came to sit with us and introduced himself and said we looked like cool people, so he wanted to meet us and talk to us, and wanted to socialize a bit. We talked for a few minutes and then offered to buy the next round. We happily agreed and kept talking for a while.

He discreetly started to hit on my wife, giving her compliments and trying to touch her frequently. I didn't mind a lot because we're at the beach and everyone is horny at the beach, plus we were drinking. I saw it as healthy fun.

Things started to escalate when he told us if we wanted to get into the jacuzzi. I really wasn't in the mood to get in since we had been in the pool and the beach most of the day, but my wife wanted to do it, so we followed his idea. We went to the pool's area jacuzzi, but since it was kind of late at night, it was closed and we couldn't get in. He had a quick backup plan and said "I have one in my room, you guys wanna come?". It made me wonder if this was his plan all along. My wife and I looked at each other and she asked me "Do you want to?" I didn't wanna be a party pooper so I said sure, let's go. Before leaving, he asked my wife what her favorite wine was and bought a bottle at the bar before going up to the room.

He had a very nice room, it was a big suite and it did have a small jacuzzi that was made for two people, so it really was kind of small. He got the water running to fill it up and opened the bottle of wine while we waited. His intentions were pretty clear by now, he wanted to fuck my wife, or at least try to. Thing is my wife was kinda into it. I know the alcohol was an influence but it was so hot seeing her like this, so I decided to keep the show going and see what happens.

Once the jacuzzi was almost ready, he took the initiative and got in. My wife took off her dress (she was wearing bathing suit underneath) and then grabbed my hand to get in with me. I appreciated that gesture. While stepping in, he looked at me and said "With all due respect..." and then looked at my wife to finish the sentence "...that's a very nice body", and we all laughed. Once inside the tension was real, it was a small jacuzzi so we were kind of tight. We were sitting in a triangle shape, so our legs were touching each other. I started to wonder what his next move was going to be. Unexpectedly, the next move was made by my wife, she put one leg on my lap and one leg on his lap, making a comment about the space being tight. I started to touch her leg around her knee and after a few minutes later, he started doing it in a similar way and then looked at me, as if looking for approval, and I approved. It was a very casual touching while we were still talking. I get up because I needed to go to the bathroom and to get the wine bottle to refill my drink, when I came back, both of her legs where on his lap and he was touching her legs a little bit higher now. I refill everyones drink and said "sorry for interrupting the fun" and we all laughed.

Once I was already inside, my wife put one of her legs back on my lap, and I start touching it again but a little higher, almost reaching her pussy with my fingers, but not really touching it. I was so turned on at this point I decided to made the move, so I grabbed his hand and placed it in my wife's pussy, giving him permission. I got closer to my wife and started to kiss her while he started to play with her pussy, then I told her "No matter what happens tonight, I will still love you the same", she then smiled and started moaning. She placed both of her legs on top of him, and he wrapped his arm around her, while playing with her pussy with the other hand. She was completely his. I sat back and started jerking off watching them. He tried to kiss her a few times but she didn't kiss back and just kept moaning. After a few minutes she came and they stopped. I cummed right after she did because it thought it was over.

My wife has out of breath and still kind of in shock, he tried to kiss her again and this time she kissed him back, very passionately. She slid her tongue in his mouth right away. They kissed for a while, I didn't expected to last that long honestly. Then my wife stopped and said "I wanna return the favor", and started touching his dick. He quickly pulled down his shorts and obviosly was hard af. She started to jerk him off but doing it underwater wasn’t very effective, so she suggested to get out. We all got out and they quickly jumped to the big bed. She continued jerking him off, and started to kiss again. I was very confused at this point, I came in the jacuzzi so I wasn’t hard anymore, but watching her enjoying like that was really hot. It was just kisses and a handjob.

He started playing with her boobs, and slowly started to take of her bathing suit. She agreed and helped him take her top off. He continued playing with her now naked boobs, and then stopped kissing her, to start kissing her boobs. She gets really turned on by this, her breasts are really sensitive. When he stopped, she quickly started sucking his dick. He started moaning and put my wife in a 69 position, took off her bikini and started eating her out. She started to moan a bit and then looked at me, she started saying “I’m sorry” while moaning louder. She said it a few times before it was only moans. I knew what was about to happen. She knew. He knew. They stopped 69ing and my wife got off him. For a second I thought it was over, but she laid on her back and opened her legs to him. It was surprisingly easy how easy his cock slid into her. Her eyes went white and she screamed a very loud moan. He started to fuck her very slowly while they started to kiss again. It was very slow love making. I was so hard by now I started to touch myself watching.

They started fucking faster and faster. My wife started saying “I’m sorry” again, screaming between moans. She started to moan louder and louder, and when he was about to cum, he got out and cumed all over my wife’s body. He cleaned her, kissed her and told us to get out. We were both surprised by his reaction, but we got dressed and quickly got out.
My wife started crying on our way to the room and kept apologizing. I told her not to worry about it, I did allow it to happen. I asked if she enjoyed it and she said she did, so kept that that and forget about the ending.

We didn't talk about it for a while, but then started to mention it while fucking. We discovered our new lifestyle and we're starting our way.