I love it when I watched a friend fuck my wife, I'd jack off or wait my turn to fuck her while she was sucking his cock. Sometimes he would fuck her in the ass, while I fucked her cunt, she really loved this. So did I.
As I have commented before, depends on who, when, where, what ... I wouldn't say an absolute no, but I would be fairly picky about it. Doubt she'd go for it, though.
I think I would - yes....
When we were younger, my wife had permission to have sex with anyone she wanted. She did it a few times, then decided that it wasn't something she wanted to continue. I still enjoy hearing about all of her sexual activities, before and after we married.
I would be happy to share her if she wanted, even though I know I would not be able to watch. Her total sexual pleasure is a high priority for me.
Yes I have no issue sharing my mate if that is what she wants to do.