I think Yuvraj loves Krishna.
Some episodes ago,when Buaji was bad-mouthing about Krishna, Yuvraj yelled at her to stop her nonsense & not to blame Krishna for everything.
Also when Krishna,Yuvraj & Uday were sitting in the garden discussing about family's reunion, Yuvraj indirectly told Krishna to forget Abhay & move ahead in her life as Abhay is not going to return anyway.
He was extremely unpleased when Krishna told him that she knows Abhay will return to her one day.
I mean, he & Krishna were living in the same house for 4 years & also Krishna's husband was away.Krishna became a friend to him more than a sister-in-law. So there is nothing unnatural if he has a soft-corner for Krishna.