We have been doing this sort of thing a very long time; our relationship has evolved through cheating, hot wife / cuckolding, to our current poly-hybrid situation. Me, my wife KK, and three other men co-habit our primary residence, so sex, kinky sex is an ongoing constant. That said:
Sometimes I get so turned on, mind blown, watching KK fuck that I experience a spontaneous. hands-free orgasm and ejaculation - from just the visual aspect, the sounds, and scents.
Whether I join in, wait. just watch, that's varied over time, the circumstances, and so on. Most of the time I watch for a while, let myself get hard, enjoying what she's experiencing. At home, I almost always join in at some point. Her favorite thing in general is having sex with two or more men at once.
She gets incredibly into it. In part, like performance art. In part, she just loves cocks and cum.
We all go more than once with KK, until everyone's balls are pretty much drained. She could probably keep going, way beyond what we can give her.
KK is "business sexy," very classy, but subtly improper in public. She is simmering hot all the time.
I have been chasing the "spontaneous, hands free orgasm/ejaculation" for years. I cum so quick I have always thought it would be easy for me. Never experienced it yet. Someday, I hope.