My gf and I met in business school a years years ago. I was 28 and she was 26 at the time. The first time we ever had a three way was with a bi guy who was (and still is!) a really good friend of ours. He was a fit, former college swimmer who was objectively very attractive. My gf got really turned on when we both took her and eventually she asked him to suck my cock.
Neither of us objected and he gave me an amazing blow job. A few nights later we were hanging out and he ended up telling us he wished I’d fucked him. That surprised me since he could pick up literally anyone and I have no clue why I was special enough to get him turned on. Eventually my gf went to bed and he brought it up again, and he started to rub my cock. I pushed him down on his back and fucked him while jerking him off. I pulled out and both of us came on his washboard abs.
It’s been our secret since :)