I write what I like to read, and I enjoy love triangles in YA and adult fiction - not to mention in other media like TV, opera, theatre, and even in video games! I relish when dark and compelling characters compete for our protagonist's heart. The doubts, the uncertainty - the jealousy! - can be breathtaking.
I enjoy a good cliffhanger. As a reader, I relish that nervous feeling you get when you're engrossed in a story, but in the back of your mind you're aware that there aren't that many pages left. How will it end? Everything can't be wrapped up! This can't end! Then it does, and your heart seems to stop.