for me it did start then, whether he knew it or was willing to admit to himself is something else. i dont think he realised it but no matter what he knew she was an innocent and had nothing wrong and i believe the only way he could go through with it was due to the fact he had started to fall for her.
it is also on this basis that kk stayed in punj house with everyone doing their best to get rid of her including rahul. she believed that her anurag was in rahul and that he did love her.
and this could be the cux of it did did rahul forget that he was rahul punj and had come to kolkatta just to get land for his girlfriend? did he become so immerse in being anurag and falling for kk that he almost forget why he was their?
thats what i believe and that when he went back to being rahul part of him still carried his 'love' for kk and that was what kk was looking for and she eventually became rahul love too.
big thanks to elysia who originally came up with the idea-thanks sweetie