If you want smutty vanilla romance, go and read "Velvet Kiss" by Chihiro Harumi. If you want cheating done properly, go for "Usotsuki Paradox", where two-timing actually makes sense*.
*I had proper review explaining why i think that's the case, but unfortunately some comments were blasted to oblivion (or somewhere) after integration with upcoming oh-so-badly-needed forum section.