long and useless

I think love triangles are so prevalent precisely *because* it's hard enough to find even one person, as you point out. On some level, all love stories are about wish fulfillment, and I'm sure there are lots of people for whom the idea of being so irresistible that two people are throwing themselves at/fighting over you is very appealing. Same goes for the idea that you're the one breaking hearts by choosing from multiple options instead of having your heart broken by loving someone who doesn't care for you back (which is far more likely what happens in RL)...