I've done all 3. Just really depends on the situation. If he wants her to have a 'boyfriend' because he is gone for work all the time, then one on one is fine. If he wants to see her get satisfied, and see the bliss on her face, him watching is cool. If you are looking for some fun on the side without your husband knowing, as long as it doesn't endanger either one of our lives and/or work, I'm down.