Doctor woh is such a confused character.
He claims to be a psychiatrist and knows that katha is hiding something behind her smile. But he jumped at the opportunity of getting close to her by getting engaged. He didn't care to ask questions at that time. He notices they are not like other normal couples but that doesn't stop him from living with her in the same house.
And Katha devi, inka to kya hi kehna. Not just doctor woh and his daughter, katha is making fool of whole family. How many hearts she will break for fulfilling her brat son's whimsical demands.
Aarav is unhappy because robin hurt his mother but katha didn't even once cared to explain that despite being hurt she forgave robin and she loves him and wants only robin as her life partner. The fact that in the process of protecting his mother now aarav is being the sole reason of hurting his mother will be devastating for him once he realise it.
Confused, shallow and honestly selfish. He is as much taking advantage of Katha as she is taking his. He knew her son was struggling and she was vulnerable and lonely because of it. And had no qualms in taking advantage of this fact to fulfill his family dreams or attraction or whatever it was. He knew Aarav was fond of him and he exploited that to also get close to his mother. Not saying that Katha was not at fault here, but this doctor is so not doodh ka dhula. If he had been some upstanding, moral hero, he would have insisted on them taking some time themselves to build a relationship to see if they had anything in common beyond their kids. If they can work together as a couple or just be nothing but parents.
All the mistakes Katha has made in handling Aarav regarding Viaan are just too numerous to even say here. Honestly, it deserves a separate post. Why she couldn't explain anything to him without talking about ONS is beyond me. She should have strictly told him to not meddle in adults' affairs and to concentrate on his own life. Whatever happened between her and Viaan was her concern and he had no business hating or being angry at anyone. Have no idea how he is able to hold onto such baseless resentment and anger for someone for so long without even knowing the reason.