I already am married (with children), and am quite happy in a monogamous relationship, as is my wife. However, we both know (and know of) several "couples" of three people. They seem happy and the children seem happy. It occurs to my wife and I that perhaps it is possible to love more than one person. Why not?
I also disagree with your comment that a male and female parent are the best option. I know two young children who are being raised by a lesbian couple. They are doing a great job, better than many male/female couples I know.
Why are three parents automatically bad, if everybody loves each other?
I thought it was an interesting thing to ponder. Don't you?