Changing genre gears?

So, I've written a lot of different genres in the twelve years since I discovered my passion for writing. I've always leaned toward SFF, but I've written whatever fancied me at the time, be it historical fiction, dystopian, suspense...

And then, I met the man who would later become my husband, and between the two of us we created a huge fantasy world, and discovered a story big enough for nine books and characters interesting enough for their own short stories beyond that. This has been our brainchild for the last five years, and we're satisfied that the core of it is done. (the short stories are mostly unfinished, but my priority has changed to getting the first book ready for submission)

Except now, I've become so comfortable in that fantasy world of our own creation, I find it very difficult to write anything else. I have ideas for other stories, but I have a tough time fleshing those out into something workable.

Has anyone else had this predicament? And if so, any advice on changing gears after you've been set on one concept for so long?

Yeah, I have thought that perhaps it would be easier once the fantasy project is really done. It just struck me as unusual that I have trouble changing gears now. Even in the middle of writing this fantasy series, I was able to take a month or so to refresh myself and write something totally different. But now I can't seem to manage even that. Before this series, I changed genres all the time, even juggled a few different ones, swapping when writer's block would hit. It's weird for me to not be able to do that now.

But I am trying to work out the first manuscript for submission, so that does really take the spotlight. As far as writing down the ideas, my problem is, at first they're very raw, and I'm not likely to remember them as well from just a memo to myself. I remember scenes, or 'snapshot' moments. I try to write those out, then I can go back and pick up where I left off. I have mountains of post-its and the like with story ideas, and so many of them are empty of meaning to me now. I remember them being powerful at the time I wrote them, but not why, because I forgot the image in my head that went with the concept.

My issue now is that I can't even concentrate on scratching out a snapshot of a new idea like I used to. And I guess, while it isn't a high-priority crisis, I worry that it's going to persist. And while I fully believe that our series is hands-down the best writing we've ever done, I want to be able to move forward.

Egad, I'm such a whiner... I'm so glad the folks here at the Cooler are an understanding bunch...

That's the confounding part, though. I feel like the story is complete, barring some fun side work and not-so-fun main revision. And the side work is mostly my husband's, as I'm not nearly as savvy with the characters in question. (I get revision duty because I actually have the time for it)

Wait... could it be? Is this writer's monogamy? I can't get other stories to hold my interest because I'm committed to this one?