There's a lot of that sort of thing in comics. The Green Arrow storyline you may be thinking of: Ollie (Green Arrow) was feverish and delusional and slept with a Dragon Lady type name of Shado, thinking she was his live-in girlfriend Dinah. This was considered "cheating" by the author and all characters involved for years, and is still thought of as such by most of the fandom.

Then there was the Nightwing storyline, where an alien shapeshifter took the form of his girlfriend Starfire, and they had sex, and Starfire broke up with him for cheating on her.

Then there was the Superman Porno Tape thing, which has pretty much the same connotations....

Really, there's a lot of that sort of thing going around in comics.