Would you

Off limits in my book. I suspect my ex best friend did . My wife swears up and down no but I'm 95 percent sure. I have wish bad I'll on both if they hooked up . She got cancer and he homless and walk like a hunchback now.

My wife and I had sex with a good friend couple, it was fun. My wife and I were 42 at the time, she’s been best friends with a girl since high school and her husband and her one night got drunk with us at a party. We swapped partners dancing, it led to touching and kissing, and sex with each other’s partners. It was supposed to be a one time thing, but it wasn’t. Her friend and I started hooking up regularly for quick sex, and we found out my wife and her husband were doing the same. It was some good time for about two months before the ladies put a stop to all the fun.

My husband and I swapped for the first time during the covid lockdown with our older neighbors. My husband was 29 & I was 26 at the time. Our neighbors are early & mid 50s, have professional jobs and in great shape for their age.
We were invited over for a secret cook out by their pool. The alcohol was flowing and everyone was flirting. They broke the ice and told us they were swingers and their summer plans got canceled with the group they vacation with. They asked if we'd be interested in swapping. They assured us they'd never try to break up our marriage and they had plenty of condoms available if we agreed.
When I first got married 4 years prior, I'd never thought I'd do something like this but at the moment it just seemed thrilling and fun. We agreed and we are so glad we did!! We still swap with them a few times a year and we've also went on vacation with them with their friends.

Six years ago, I had sex with my friend's husband that we'd known for 20+ years. It was a one time fling. We've kept it secret and thankfully things have never gotten weird or awkward.
It was the first year after all our kids had moved out so we decided to rent a beach house.
My friend went to a play solo. I stayed at the house to enjoy the beach. My husband and her husband came back from golfing with a couple bottles of bourbon. My husband had too much and we helped him to the bed.
I'd had a few glasses of wine and feeling buzzed. We've always flirted when we were alone but this time things got heated. I sat on the railing and he stood between me.
The next thing I know, his penis was out, my swim bottoms were pulled to the side and he was going in and out of me.

Personally, no unless invited by both. Not worth a friendship over a piece of ass! Just my 2 cents. Let fantasies be fantasies. Unless he's a shit friend, then whatever.