Ok, what an amazing start to your first story! 

This set-up is simply buzzing with potential, and makes me ask so many questions! That's not a bad thing, but good because stories like these thrive on the suggestive. 

Nonetheless, I'm super curious and will ask my questions anyways: 

- What is the nature of shrinking in this world? (It seems like a shrinking virus setting, but I could be wrong.)

- What is the status of tinies? Are they treated as people or objects/inhuman? 

- What exactly is Josh's relationship to Kelly? (The fact that Kelly wants to get Amanda back together with him suggests they at least aren't romantic, maybe more of an owner & pet/toy arrangement?) 

Whether you decide to answer my questions or simply leave it all a mystery is fine! 

Regardless, the idea of a woman being in possession of her best friend's ex-boyfriend as a tiny pet (or roommate?) that she casually uses as a sex toy is incredibly erotic. The fact that she can go from casually talking to that same best friend about how she uses him, and then immediately pivot to excitedly planning on getting them back together romantically is also insanely hot! The seeming lack of any taboo around this suggests something about how tinies are viewed/treated in this world, but I could be wrong. 

I can't wait to see where this goes! Keep up the great work! 

I see there's already a second chapter, so I'll read it now and leave a review as well :)