This is a conjecture formulated through experience. Ever since Karishma and Upen started their dalliance there have been a lot of theories about what is actually happening.
For those who haven't read my other posts, my stand on the matter is that they are both being honest and there is no 'bigg' conspiracy about this. I might be wrong of course since they're both actors and it is their trade to pretend.
But in case I am not wrong and in case they both really do love each other, then the issue comes up that Karishma has a boyfriend and she's being unfaithful. Also that while she 'used' the boyfriend card to repel Rahul Mahajan, she had no issues in getting on with Upen.
Let me narrate an incident. A few years back when I was working in Noida I had a colleague who was the same age as me. She used to wear a mangal sutra. Everyone including me assumed she was married. Over the course of a few months we became good friends. It was after that I realized she was actually single. When I asked her why she wore the mangal sutra she said it helped reduce the unwanted 'proposals' she got from men.
KT of course does have a boy friend. But as the incident above illustrates it is a woman's prerogative whether or not she wants to use her 'in a relationship' card to ward off unwanted men. Karishma used it to try and keep Rahul at bay (not that it really worked, he said woh uski problem hai), but in this IMO she wasn't wrong. Where she was wrong is the way she overdid it in the phone call. But I digress.
Next comes the issue of her being unfaithful. For a moment setting aside whatever issues she might have had with her bf, thing is nothing justifies being unfaithful. She certainly should have spoken to him before making a move with anyone else. I can only imagine how it must have been for RC if he still has feelings for her, when he saw her with Upen on the show.
But keep in mind that that is something Karishma is trying to prevent. To the best of her intelligence. I really feel that the reason KT has been noncommittal to Upen in front of housemates but close to him in the night is because while she loves him, she is still uncomfortable calling herself 'in a relationship' with him till she has formally broken up with RC. Of course she might and probably will cave in to pressure in time and commit to Upen. But as a woman, I can almost hear what must be going through KT's mind.
'I have a boyfriend outside, Upen is a really good friend'.
'Darn it Upen proposed to me. I have a boyfriend outside. I don't knw what to think. I have to focus on the show. I'll deal with this once I'm outside'.
'Upen is back in the show. And he's serious about this. This time most likely most of the viewers have already heard him. And I really do love him'.
'I have a boyfriend outside but I cannot ignore what I feel for Upen. But it will not be fair to my boyfriend if I decalre myself in a relation with Upen before I talk with him'.
'Everyone is misunderstanding me and pressing me about Upen and me. I wish all the housemates did not keep going about this. I wish Upen could take it easy. I really want to close things up with my boyfriend before moving on with this'.
'Stuck between a rock and a hard place. Doing the best I can. It is going to be ugly breaking up with my boyfriend when I go out now but this is what life is about'.
TLDR...well, you just have to read the post. 😛