I found myself in an almost identical situation. However i was lucky. I can still see my wife release his cock and remember feeling strangely turned on by the sight of his huge erection and my wifes hands on it. I watched his balls tighten as he entered her and started thrusting slowly. I asked him to pull out and slid my now bursting erection inside her. I was so turned on i felt my load rise and i shot my load powerfullly with the first stroke. Id never cum in front of another guy and it was very intense. I then watched his huge cock thrust in and out and watched him shoot his load
My wife and I had a really good friend in the Air Force in the late 90s who I should have tried to share my wife with. His name was Steve and I saw him in the shower on deployment and he had a cock that hung down between his thighs, I was impressed and I am straight. I know my wife and had it dawned on me I could have told her how well endowed Steve was and hinted about a threesome with him and I am certain she would have said yes. He was single and hung out at our house on base and my wife and him got along great so there was a little bit of chemistry between them already. God I could just imagine my wife with him and seeing his cock for the first time and being in awe of his size. From there all i would have to do is sit back and watch because my wife is not bashful and she would have gone over to Steve grabbed his cock and started sucking on it. And she would have been the one to guide Steve to our bedroom get on our bed and lie down naked with her legs spread with her pussy out there for the world to see and ask Steve "what are you waiting on." i can only imagine what my wife would have looked like taking Steve's big cock and having him get all the way inside her and fucking her for the rest of the night.