Neither Shiva nor Raavi would involve in extra marital affairs or cheating. Even most of the peope won't even want to imagine that. If u want to do something different, then u can make a love triangle story, ya u can say that raavi was already in love with Dev and many stories were based on that, that is shiva, raavi and dev's love triangle. I know, for this u can make a role reversal of Raavi and Shiva, coz Shiva didn't have any other girl in his life other than Raavi, so it will be different and unique too and we could get a jealous Raavi, but don't bring extra marital affairs. It's a request, rest is your choice.