without willing consent,
that is... if you are coerced, confused, manipulated, dominated, tricked into consenting,
i dare say, you will experience a feeling similar to what we survivors are going through.
without trying to offend anyone here,
doing something sexual that you do not want to do is hardly too much different from sexual abuse... when you think about it.
there were many times i consented to sexual activity i was not "into" for the sake of "quid pro quo"
(that is... if you do______ then i'll do_______)
as i stated earlier, the end results were ALWAYS negative,
regardless of the pleasure experienced.
sugar tastes great, but it rots the teeth and wrecks your health if not properly consumed.
you would not be doing yourself, or your partner, any favours by submitting to pressure in this situation.
there is also the dynamic of the soul and personality of the 3rd person. this is human being, not a fantasy, so they will have their own perspective on this experience, should it occur.
have you considered what introducing that mystery into your relationship might do?
my short answer is... don't do it.
but i have very little information to go on,
and i am not you in your situation.
i wish i could tell you more.