8. Ivy, Derek & Karen - Smash
The first episode of Smash appeared to hint at the possibility of a relationship between potential Marilyn Monroe star Karen Cartwright and stage director Derek Wills - something that became a reality further down the line. But things grew complicated when the other woman vying for the role of Marilyn, Ivy Lynn became romantically involved with Derek.
The on-stage tension between the two actresses was magnificent enough on its own, but throwing in a love triangle only proved to intensify the drama further, which made Karen and Ivy's musical numbers all the more powerful. Moreover, on a subtextual level, it gave both Ivy and Karen more to work with on stage, due to the fact that their own love lives were becoming as colourful as the real-life Marilyn Monroe.
A change in direction for the show's second season put an end to the triangle, as Derek chose to do the right thing and stand by Ivy, who was now carrying his child, which was the perfect conclusion to not only the show, but to this three-way rivalry.