I have a novel that I've been querying. I've gotten a list of requests followed by some very helpful rejections. So, now I'm in the process of revising that novel. One of the comments I got was guy #1 wasn't fully realized, so I set about making him more well-rounded. I ran into road block after road block. Then, I realized the problem. Although this novel can stand on its own, I've created two sequels to finish out the story. The first sequel has been outlined. The second is only vaguely realized. Here are the basics.
Book 1 - MC falls for guy #1. He's fabulous, but then she realizes she loves guy #2.
Book 2 - Guy #2 goes away. After a long period of time, she decides it's time to move on and tries things again with guy #1. Guy #2 returns.
Book 3 - She never goes back to guy #1, and she and guy # 2 live happily ever after.
Last night, I started thinking, "What if guy #2 doesn't want her back? What if guy #1 is who she chooses in book 3?" That's when things started to clarify for me in book 1. I'm not saying the problem is completely fixed, but looking at the unwritten has definitely given me renewed inspiration for my rewrites in book 1.