Yesterday's episode gave out rather strong hints about this. When Ruchi said something about her mother's advice about getting things easily in life, Adi's dad said that it reminds him about the things someone very close to him used to say.
Later, he tells the girls that he's from Allahbad to which Rohini replies that her nana's home is in Allahbad too!
I'm sure all this portends a past relationship that could have existed bt Radha and him.
The interview on India Tv that I watched a couple of days ago included the actor who plays the role of Adi. He said that Adi will get very close to Radha and her family as the bond, love , affection and values he observes there is something he never witnessed or experienced in his life.
This indicates that his own family life isn't hunky dory. Maybe the father too might seek comfort with this family. He seems to have already bonded with Ruchi...I liked the way she went back to seek his blessings...her future FIL??