Nyssa, I am a mod, but still using training wheels, I cant see a split thread option like I get on other sites - not to worry - I'll let you let off with a warning.
Someone can probably give you you a couple of regex's to fix the broken lines
I'm more comfortable fixing things like that without the html markup - so I'd convert to formatted text and use an editor like Notepad++ (or the one I just found called Bowpad - Scintilla wrapped in a pretty ribbon) and then convert that back to EPUB.
BR