I watched the first few times, and she also had some solo experiences with her encounter partner.
The very first time I was present - it wasn't a planned experience, but we had been working up to her being with another man for at least two years. It was still an overwhelming experience, even though I wanted it to happen.
It was simultaneously what I was expecting and hoping for, at totally different than what I had imagined.
If I had planned to participate in a threesome, I likely would not have been able to perform adequately the first few times. Reflecting on it, we probably had six to eight encounters, about half of which I was present for, watching, and the other half with her solo. Now I participate in about 75% - 80% of her encounters actively.
I almost always join in. Our first 3-some was fantastic, our new friend was very talented and with both of us giving her our full attention she was going wild with orgasms. I just love seeing her that way!
3some seems more natural, whether it be MFM or FMF. It surprises me when I hear of younger people considering a purely spectatorial scenario for the BF or husband at what many would consider a foundational, formative stage of their relationship and lives. When you think of the intensity of some of the feelings -- jealousy, possessiveness, insecurity -- that can accompany young love, it just doesn't seem like something most folks would build on.
On the other hand, things have changed, even in the up-tight U.S. I do think younger people are more relaxed in their attitudes about everything, including sex, and far less concerned about what others may think.......perhaps more willing to just go for it when it comes to thrills, the things that may turn them on, and experiment in whatever way far more freely. If they know what they want and both want to, more power to them.
And a 3some can always evolve to watching if that's what works for them. I say 3some AND watching!