We all are irritated by Pakhi's behavior. I am one of them. It could be also because we ship SaiRat and anyone who stands in between will be hated :) We tend to vilify the third person, so it becomes easier to like the favorite pair.
I think Pakhi's character is very simple to understand, and a very real one too. She is a decent human being, who might not be selfless as Sai but definitely not an evil person. I thought of understanding her character iff her life would have gone as per her wishes. What would she have been?
Even then, I could only imagine her as being possessive, selfish and temperamental which are common traits in most human beings, not evil. However completely opposite of what Virat wanted as a family man. Why? I could not imagine her as an independent working woman who works alongside Virat and takes care of his family members. Why? Not that it is wrong to live separately from joint family if one doesnt like it. It is completely OK for a wife and husband to come out live on their own. But I somehow feel that she will be this kind of a person who limits her relationship with just Virat and her parents. Why?
I think one can gauge a person better by seeing how they respond in unfavorable situations. Not when everything is going well. So is Pakhi's current behavior actually a mirror to her actual behavior? Why is she not moving past Virat? I come to understand her behavior is more possessive and obsessive rather than understanding and adjusting, with or without Virat which again is not evil, just bad.
Why the obsession not love?
She attached so much value to Virat that she thinks he is the most valuable possession. Whatever little I understand of the human behavior, we all are prone to attach value to one thing or the other and feel terrible when someone else has it but not us. Be it a handbag, or jewellery, a house or a person. Same is the case with Virat for Pakhi. She had tremendous attraction towards this guy who she thought was 'perfect' for her. She attached a brand value to the man named Virat and made him raise to something unachievable. May be Samrat is a better person, objectively speaking and as Virat mentioned several times, but in her eyes, no one could match Virat. Extreme attraction and fondness for something can cause that kind of attachment towards it. The loss of such thing can only cause envy not heartbreak. For her Sai has got something valuable which she lost narrowly. So the envy. She sees Virat only as possession. Thats why she gets agitated when Sai claims her right over him. If it was genuine liking for a person and a heartbreak, it will heal over time. May be you cannot move ahead with another person, but you dont hurt the beloved one.
So my point is, even if Pakhi married Virat, she would have been extremely possessive to the fault with Virat. He was a desirable possession, which like any other object fades with time. Just because he is unavailable now, the possession became obsession. And someone is having it in front of her is driving her to extreme behavior. The solution to her problem is to divert her from Virat . It is just the mind that is involved here, not the heart. The heart can be healed with time and the mind can be diverted. Samrat's disappearance is the nail on the coffin I guess. If not for that, she would have tried to move on. Hence in future, if Samrat comes back she will give a chance to her marriage. I think that is what is shown in KD.
PS: If we see Pakhi's problem independent from SaiRat, we can empathize with her. :)