Both of them loved each other before Mani arrived.
But it was the Mani who got them out of their denials.
U know.. Like they say.. "Once bitten twice shy".. That was the case with them. They're both hurt in their first love. So, like normal hearts they tried to not enter that zone.. But slowly and steadily they did love in love.. But it was because of their past that they kept denying it to themselves.
And as far as I am concerned. I always feel it was Raman.. Who fell in love first. Nothing great in it just that he cudnt help falling in love with such a selfless, loving and caring wife that he had. He constantly kept comparing ishita to shagun.. And always felt good abt it.
I feel that day when he came back and hugged ishita in the parking lot and said a I love you for the wonderful speech at ruhi's school that he cudnt attend or maybe did in the end.
Later he denied of the " I love you" and shagun was seen behind on a car. I know many ppl will not agree. But I believe.. He fell in love since then.