I always felt Dev liked her from the beginning. First time after they banged into each other on the road and when he was home , his relatives asked how his coat got dirty , the way he said "ek bevakuf se takaraya tha" there was an interesting smile on his face. Then the next time was when she got his mom to the hospital , from there began a sense of appreciation for her along with guilt that he was being utterly selfish by getting her kicked out from her job. Him noticing her as a woman was when he saw her in that yellow Saree ...when Kushal came to meet her. Next stage was - in spite of all his selfish act and trouble he gave her, she did not accept the other job offer. She stayed committed to him and his family. Slowly he was falling for her as she was so different from him at the same time she was everything he wanted. He eventually found a friend in her with whom he could be himself. And then the major turning point I feel was the accident. This bought him close to her. He was scared of loosing her. Those 30 to 45 mins spent trying to keep her awake telling his stories was life changing for both of them. And after that I feel there was no turning back. It was only a matter of time when he had to give a name to that beautiful sense of peace he felt when he was with her.
So for me its Dev who fell in love first!!