@Bhavi @ Rani - You guys are spot on... I too feel that Richa is/was a nice girl and both of them fell for each other... Both loved each other... Since they were leading a comfortable life they never got the opportunity to imagine how the other person would behave in times of difficulty... everything was rosy... Richa found the perfect guy for herself.. someone who was well-off and successful (he was the top-most lawyer). Kunal in turn found girl, who loved and doted on him...
When things changed for the worse, Richa found herself unwilling to leave her comfortable lifestyle... However she continued to love Kunal and never once fell for/thought off another guy... She was confident that there would never be another girl in Kunal's life... Till Siddhi came into his life, which was circumstantial...
Once Siddhi came into Kunal's life, Richa became insecure and this insecurity kept growing as days passed and she saw Sinal getting comfortable and coming close to each other... And that is how the evil side of her came to the fore...