I seem to have a pretty infinite ability to love.
I also have discovered that 3 relationships is near the ragged edge of my daily ability to stay sane. Frankly if all 3 weren't so committed to each others' well being as well as the relationship as a whole, a triad would be hard enough, nevermind whatever we have now (a triad with a an arm of sorts I guess).
So both points are valid. A flame shared does not diminish itself; adding fuel to the fire makes the old log burn hotter; but there's only so much fuel to throw on, or one persson may only fan so many flames, lol.
I coud see where adding more males or bi/les females could divide the labor so to speak, but maintaining a level of intimacy and connection on a relationship level between any one person and the group as a whole - 3 is my limit!