Eva,
You are so right. Radhika never had a reason to be jealous or possessive about Dev because he was always hers. Now, he pays some attention to Vishaka reluctant as it is and out of guilt feelings. Vishaka is already beginning to want to take things meant for Radhika. She wants Dev now and will start running after him as she goes after anything she wants. That's when Radhika will show her possessiveness. So, Dev will show it after meeting this guy and Radhika will do the same with Vishaka.
Really like the fact that Amma and all the obligations are now out of Radhika's mind. Losing that care-free Dev has done that to her. She is taking so much initiative now. When Dev was lecturing her about culture etc., she answered him back and then Dev was looking quite happy with that. He is now getting more attention from Radhika than he ever did. He has become her priority over even her CB duties. So, she is acting like her namesake more and more and I for one like it. Also, a mature Dev is suited to fight with this new guy as well as make sure his RP title remains intact and is not snatched. So, it will be more serious Dev who would be shown from now on. He won't be brooding after this HM, but he won't be smiling much either. He will probably seen to be most relaxed with Radhika. That is fine as you need to show growth in your characters.
Mrin will still use Vishaka as she was looking at her in a calculative way. Once her plan with Hiten doesn't work out as well, she will incite Vishaka to go after Dev. Vishaka is already ready to do that. Liked Vaishali today. But, I am wondering if it is now known to everyone that Radhika was Dev's choice and not Vishaka. Vaishali talked about it today and chachoo, Mrin and vishaka didn't look surprised. I was under the impression that Vishaka didn't know about this. If knowing this, she still goes after Dev then it is despicable and she deserves all the insults.