Last weekend, we decided on the spur of the moment to catch up with some old friends a few miles away. As they have a busy house we stayed in a local spa hotel and made the most of the facilities. I am no "gym bunny", so whilst Celeste went to the gym, I went for a swim in the pool, which overlooked the gym itself through glass panels. Whilst Celeste was "cycling", one of the trainers came up to her and they started chatting. He looked very fit as you'd expect, and was obviously flirting. Celeste seemed to be enjoying the attention. I dried off and sat on the lounger and decided to text her to see what she was up to, as she keeps her phone on her arm whilst working out. I texted something like "Hiya, you seem to be getting on well" and watched as she replied "Yes, he's cute, but half my age! :-)" I have long since had great joy watching Celeste flirt with people. It turns us both on massively and I was instantly horny. "Tell him you're going for a sauna and see what happens!" "Yeah right lol" "Go on, give it five minutes and I will get in the sauna first". With that, making sure the guy didn't see me, I made a gesture that clearly said "go on, get on with it!". I sat in the sauna for around ten minutes and was about to give up on the whole idea. I reluctantly added water, steaming up the glass windows completely and thought about what might have been. Suddenly the door opened and in walked Celeste in her bikini. A couple of seconds later, in walked the young trainer, who must have been around 25. Celeste looked at me but didn't say a word and simply nodded and walked to the opposite corner. The young guy did the same, nodding at me before walking over and sitting next to her. I sat back and pretended to be dozing, but in the poor light could easily see and hear them chatting. He was being very complimentary and she was giggling and gently pushing his arm. I noticed him turn to look at me, before turning back to Celeste and laying his hand on her leg. She laughed and leaned back a little, smiling at him and put her hand directly over his cock, keeping it there. I could see him squeezing her leg as he leaned towards her and trying to discretely cover my view, obviously not knowing we were a couple. I moved myself a little, still feigning doziness, to get a better view. Celeste was gently massaging his cock and he was clearly enjoying it as he nuzzled up to her neck, kissing it. Celeste then pulled his shorts forward releasing his generous penis, and slowly wanked him, looking over his shoulder and smiling straight at me. After what seemed ages, but was probably only a couple of minutes, he started to wriggle a little, clearly readying himself to cum. Celeste stopped looking at me and shielding my view with his back, bent down and took him in her mouth. After another minute or so, he took a deep breath and then seemed to relax his whole body. Celeste's head then reappeared as she used her fingers to wipe her chin clean, smiling at me. "Are you free later?" I heard him ask, then seeing Celeste looking over his shoulder he turned to me. "Afraid not" I said, "we're going to see some friends". It took a few seconds for him to register and he then laughed, saying "Oh I see!", suddenly realising we were together. "In which case- thank you both very much" he said, before laughing and saying, "I'd better get back to work then!- Let me know if you are back in the area, my name is Martin". He thanked us and walked through the exit. Celeste and I both laughed, before returning to our room for some fun of our own.