My wife and I have had two "rules" from the beginning with her lover, one is no sex for me three nights before she going to meet her lover (Either alone or in a threesome) and the other "rule" is that her lover must have one ejaculation before I can join the fun.
So yeah, I have watched my wife getting penetrated a lot of times and love every second of it. Usually my wife sucks her lover off and then me before we all takes a shower (To watch my wifes pretty face suck her lover cock until he fills her mouth with cum and then listen and watch her moan in pleasure before she without any hesitation swallows her lovers cum is also very high on my list too watch. ) But sometimes they just go directly too the bedroom, get undressed and lay down in bed with me just as a spectator due to our second "rule" and I watch him finger fuck her, tongue kissing her, sucking her nipples before he push himself up on his arms and slowly push himself over my wife, that just opens her thighs and grabs his long and very erect cock, pulls his foreskin back and slowly, cos she knows it turns me on, starts rubbing his cock head up and down her wet pussy a couple of times before she just as slowly guides his cock inside her pussy. A little sigh or moan escapes her when her lover trust his stiff cock inside her and watching her push her hips and pussy up to meet his cock almost get me too moan in intense pleasure just by watching it. Then he lays himself over my wife and slowly starts to fuck her while they are tongue kissing and he feels over her breasts, sometimes sucking her nipples and just enjoy my wife's willing and wet pussy before he starts fucking her.
Then, after some minutes, my wife moans in pleasure and I se her hands dig her nails in his naked pumping butt before she screams her sort of goose like scream and have her first orgasm on her lover cock. He just continue to fuck her mercilessly and I hear his balls slap my wife's wet ass cheeks for every trust he gives her and some minutes later my wife have her second orgasm, wilder and harder this time and she is totally her lovers women now. I love watching her face dissolve in lust and pleasure over her lovers shoulder when she cums and usually, not always, she have another orgasm after that before her lover, with a sort of warning moan and then a low roar starts filling my wife's very willing pussy with a huge load of cum and my wife, she loves to feel a man ejaculates inside her, cums harder and more intens than ever.
And I, shaking with arousal, loves watching that, that is still number one of my list of the things I love to watch. And of cause the magnificent feeling when I fuck her just seconds after her lover have pulled his dick out of my wife. That always makes me cum harder, longer and more intense and my wife loves me doing that, having her second cock in her pussy.
So yeah, I totally knows that feeling.. 🙂