Like most of my secondary characters who work out on the page better than even I expected, Rain and Farlae want their own book. Specifically, the story of how they met, survived disaster and fell in love (evidently the details I sprinkled around in Evermore were not enough to satisfy them.) They already picked out their own song (Two Princes by Spin Doctors) and Rain was making me listen to it at least twice a week. I outlined their backstory before I wrote Evermore, and I've been adding things to it ever since, but that was just making things worse.
When the same situation happened with Squilyp in Beyond Varallan, I let him live instead of bumping him off as I'd planned and dealt with him in other ways. This is the same reason you Darkyn readers will be seeing Rain and Farlae again in Twilight Fall. I gave them some story space primarily because their presence served the story, and to reveal a little more about their respective talents, but it was also a deliberate anti-distraction tactic on my part. To be frank, giving them more story also got them out of my damn head so I could concentrate on other things (P.S., they still want their own book, but Rain is presently playing a Strip Monopoly marathon with Farlae, and they both seem to be satisfied -- for now.)
The more life you breathe into your characters, the more they come alive on the page. The down side of this is that they also become more real and important to you. These are the type of characters who are always waiting in the wings, in some cases looking for any opportunity to tell or continue their story. Over the span of your writing career you can rack up dozens of characters like this, and unless you want to write one book with four hundred and ninety-three sequels, you have to find a way to deal with them and placate yourself.
A few other ways I deal with distracting series characters:
1. I write a short story about them. This is not as satisfying as giving them a whole novel to play in, but it takes less time and still gives me a chance to write out whatever's bugging me about them.
2. I send them off somewhere so they can't get involved in the current story. This is why Garphawayn is on Omorr at the moment with her sons, and Jema and Thierry are house-and territory-hunting in the Carolinas.
3. I outline their novel and/or everything I want to write about them. This works best with characters who haven't yet developed into full-blown major distractions, and may be the best way to deal with any character with serious distraction potential.
4. I bring them back with cameos or their own limited subplot thread. This works pretty well for characters who like Rain and Farlae are too developed to be placated with method #3. This is also what made Squilyp become such a pivotal character in StarDoc, something I fought for a while and then just caved in, accepted and worked him into the series plan.
5. Worst case scenario, I kill them off. This is a last resort only, and reserved for those series characters who threaten to derail and wreck things permanently, which to date has been only three (although Xonea has on more than one occasion come very close to being number four.)
The other thing to think about with character distractions is why you're being distracted by them. They may represent something you haven't expressed or addressed in your work, such as a subplot that didn't get enough attention or an unseen hole in the main conflict. Also, look for characterizations that suffer by comparison (i.e., if your secondary characters are more interesting to you than your protagonist, you can bet there's something wrong with or lacking in your characterization of your protag.)
How do you deal with character distractions?