I thought it was actually sweet of him to decide that. Not that Jiwoo minded bottoming. He was more than willing to do so (Β κα΄κ)
I mean, I think he wanted to be the bottom, not hurting Jiwoo was a reason but that just doesn't seem to be the only thing. He was crying and all because he thought that he wasn't cute anymore as he grew super tall.
This is a huge spoiler though. I read it in the raws first and the reaction I had was priceless. I wouldn't want anyone to be robbed off of that.
Woah I didn't expect that but dongchan was actually the bottom it was good. I don't mind either way.