Sometimes this question is asked in such a way that we may feel defensive, perhaps by people who are judging it before they fully understand.
In other instances, this question may be asked by a spouse or friend who truly wants to understand.
I'm interested in hearing anyone's experiences or thoughts.
I was asked this question (or a version thereof) and it was basically asking "why do I need/want someone else?"
In my own case, it wasn't because of any unhappiness (which some people associate with 'seeking out someone else', ie. cheating) in fact I'm happier than I've been in a long time. The reason why I sought out someone else, was for the 'experience' at first, something both my husband and I wanted. Then we both discovered that it was possible to have a relationship with more than one person, and to fall in love. So for me, if I were to seek out another it wouldn't be to fill any void, but it would be for a chance at even more love and/or more happiness.
When some of my family has asked, they haven't been a frame of mind to truly listen to what I'm telling them about why I'm not monogamous. That does shape my answers, typically making them brief. But the answer is simple, "Because it makes us, and everyone involved, truly happy"
P.S. I also wanted to add that when I was discussing this with a very good friend, I joked that the "3 hours a week I don't spend at work or with my men needs to be filled with something"
Truth be told, the time factor is a major concern, but you make time for what's important, right? If everyone's needs can be met, then maybe it can be something worth pursuing