I last remember reading this at some point this year. I cant remember where I saw it, but I'm relatively sure that it was either here, OmoOrg, or ABDLStoryForum - I know that this is an insanely wide net. The basic premise is that a guy who is into the abdl scene is transported into a world where diapers are the norm. While there, he manages to catch the eye of a girl (Rachel, I think), who winds up making him a pair of briefs. By the end of the story, he is back in the normal world, though Rachel is still his girlfriend.