Basic Idea involves Twin sisters, and one of the sisters boyfriend.
Basically, One sister has a boyfriend, and the other doesn't. The Other likes her sister's boyfriend just as much as her sister does, and decided to play a trick, getting him to believe she is her sister so that she can go out on dates or sleep with him.
Eventually, of course, she/they will be caught.
Soo...yeah..that's just a basic idea...we can add on more if you want.
PM me if interested.