Falling in love with a married man is not supposed to happen. Yet, in Tellyland, it is not at all uncommon. In TP now it is Rhea; earlier it was Tanya.
The reasons that Rhea finds herself falling in love with Girish have been mentioned earlier. I am not going to restate them. I am only going to emphasize two.
Reason one:
For Rhea, Girish is usually older and therefore, in her eyes, more experienced and mature. Rhea considers herself more mature than others of her own age. The trauma of losing her parents at a young age and the need to fend for herself has made her "emotionally" grow up faster.
So it often happens that a girl who is growing up much faster than the boys around her thinks that they are childish and silly and finds herself dreaming about the charms of older men. The married man she has contact with, in this case Girish, seems so much more grown up and excitingly mature that he has become the object of her love rather than the boys of her own age who are still just "children."
Rhea in her infatuation is doing (IMO) some foolish stuff - like those "shahiri notes" and birthday party preparation. Now, she is thinking (with a little push from Anuja) perhaps of running away with Girish. Hopefully, she will outgrow this crush for Girish soon before she does something drastic and humiliating. Tanya was ready to murder Pakhi - I hope Rhea does not indulge in that kind of behavior. Although I call her behavior foolish - for Rhea, right now, her emotional entanglement with Girish is for real.
Personally, I do hope her bonding with Pakhi happens quick (as hinted in the precap). Because, she has no one she can talk to - about her feelings for Girish. Rhea is playing a dangerous game with Anuja. We all know how devilish Anuja can be. Once she gets to know that Rhea plans to destroy Lavanya's marriage she will torment Rhea forever.
Reason two:
We know that Indian society scorns the other woman. Marriage is such a sacred institution that any girl/woman who breaks a marriage is held in contempt by most people.
So, why are the CVs showing a girl falling for a married man?
I can think it is to convey that Rhea is so deeply troubled that she is unconsciously getting herself into disgrace as a way to hurt Veer. Somewhere deep in the recesses of her mind Rhea wants to socially disgrace Veer. She wants Veer to be held accountable for the breakage of Girish-Lavanya marriage. Perhaps because Rhea thinks that Veer was the cause of unhappiness in her parents married life?