The re-entry of the son into the father's life is a very timely move as it serves multiple purposes. Firstly, it moves the plot along. Following the brief lull after Ishita's marriage to Raman, and the winning of little Ruhi's custody, Aditya's return oils the wheels of the plot, and gives it a momentum and flexibility that it would otherwise not have gained. Secondly, Aditya's entry helps keep the villainous beings, Shagun and Raman in play. Without Aditya's presence also they could create trouble in Raman's life, but with him right there the possibilities of torturing Raman are both natural and endless.
Finally, and most importantly, Aditya, the son, serves to illuminate the dark, forgotton, and cobweb-ridden corners of Raman Bhalla's psyche. Earlier, Shagun was the fuel that powered Raman's life. He lived for her totally and completely. She was his muse, she was his love; she was his everything. Once when Shagun's dramatic accusations put Papa Bhalla's reputation in jeopardy, Raman sided with his wife, without even hearing what his own father had to say about the matter. Raman's bespectacled love for Shagun shut out the entire world. So in love he was that he was oblivious to everything --his parents' feelings, Ashok romancing Shagun away from his life, right in front of his nose, and even Shagun's growing growing frustration and hatred where he was concerned.
True, Raman has got over Shagun and has no passion left for her whatsoever. However, this passion has not gone; it has been merely displaced on to the son. Like Shagun was several years ago, Aditya is now Raman's weakness, his Achilles heel. Although his spectacles are off, Raman's vision is still myopic. He has the same blind adoration for Aditya that he had for Shagun in that nothing exists other than Aditya. He could not bring himself to play holi to please the little daughter that begs him to play with her; yet, he goes to the holi event without any compunction just to be able to interact and play with Aditya. All of Aditya's faults, his sarcasm, his condescension, his hatred, and his thinly veiled anger against him are either unseen or excused. The love-lorn husband who betrayed his father for his wife has donned a new avatar of the pining father who, is totally capable of betraying his present wife for the sake of his son.
Aditya's presence, like the sun, shows Raman in an interesting light --a man who is terrified of intimacy. In other words, Raman is more in love with the concept of love, rather than with the loved ones in his life. It is easy for him to idealize and have strong bonds with personalities that are "absent," be it Shagun or Aditya. It is easy for him to want what he cannot really get, while the people, such as Ruhi, who are there all the time loving him unconditionally, are largely ignored or taken for granted. Had it not been for the custody scare, Raman would perhaps have continued to ignore Ruhi.
With Ishita, Raman has met his match. She is neither absent nor devious, and does not play the games Shagun did. Ishita's personality often keeps Raman shaking his head in confusion and calling her a "pagal aurat." The reason that Raman has difficulties in bonding with Ishita is as much due the mistrust drilled into him by Shagun's betrayal, as because of his own dread of bonding with someone who is capable of reciprocating the depths of his feelings.
Aditya will play a cat-and-mouse game with Raman, repeatedly catching, maiming, and releasing him. Ishita will doubtless tend to his wounds, even if he shuns or betrays her in the process. The question is when will Raman know the true worth of the gem called Ishita in his life? We all wait and watch.