??

Maybe give Scars Are Red, Bruises Are Blue a shot. It's on Wattpad and it's by a writer called jensenshackles. I don't have the link right now but if you type it into Wattpad's search bar it's the first thing that comes up. :)
They're not in a relationship at the start but Dean does bully Cas (it's a highschool Au). Not sure if it's exactly what you asked for, but it's the closest thing I could find and it's a great read.

Thanks