"I haven't been working on that project for awhile. I fell in love with another idea." If you've seen the someecards image of someone saying that a woman (or a writer's) mind is like having a couple thousand tabs on a website browser open then that'd be a good description of not just myself but other artists as well.
Some writers can only work on one thing at a time, especially a large project. Others initiate work on several ideas that may hit them out of the blue. I've had friends and/or overheard other artists say how they were plugging away on one thing to get struck, as if by lightning, by something else and now that new idea is the shiny penny they want to focus their efforts on.
Unlike the "Falling out of Love" with your work post from a few months back, this is more about a balancing act. When jumping from one work to another requires a complete mental shift along with solving the puzzle of more than one work.
When I work on my Collection (my long-term gestating baby) I not only have to be in different POVs for each character but rely on the link of what keeps it together as a linked anthology. But then there's the young adult thriller I'm working on and the essays I'm drafting, not to mention restaurant reviews, blog posts, and flash fiction I'm revising. Each project requires me to shift gears sometimes drastically and it means that while I may be working on one project a fix may hit me for another. It means that while I am forcing myself to sit down and draft an essay where every word feels painful and dull I may be thinking about that work that feels more exciting to me at the time causing a lack of focus for what is in front of me. It's not unlike having a fantasy of a celebrity while on a blind date. You may not be totally uninterested in the person in front of you but you're certainly not completely focused at the moment.
Tackling multiple projects can be synonymous in this way. Each day brings a different mindset and progress may seem slower on one project than another simply because the enthusiasm and excitement has waned. Is it dead in the water? Not at all. It's really attributed elsewhere for the time being.
I haven't felt like I was "cheating" on my Collection in a long time, if ever. My mind is one that doesn't shutdown, even when it needs rest. I cannot focus on one story, which is why my longer projects, novels in particular, tend to have multiple POVs. I like the challenge of thinking outside the box and also of reshuffling my focus to be able to tackle more than one thing. It can create a seemingly never-ending list of writing. One that feels daunting rather than thrilling. But for whatever may or may not work there's always the understanding that the challenge of writing is what stimulates and keeps you going.
If you have one work you feel you're neglecting--and this could very well be because it's a pain in your a** at the moment--don't freak out. Don't feel that you're cheating on it with something more appealing, easier (or not), something that feels fresh and destined for print while the other project you may have lived with longer may be something that is losing its luster. I've felt the same way. There are days when I've wanted to forget my Collection and focus on the essay that feels like it'll be complete sooner or the flash fiction that is oh-so-close. At times my Collection is a monster and it's okay that I may need a break from it every once in awhile. The work will be there, it won't finish itself, but forcing myself to do it when I'm thinking myself distant from it doesn't always work. The space I've needed in real live relationships is one I've also needed with my work. "I simply cannot deal with you right now. I love you. See you later."
It's not a good-bye. It's simply a break.