Sorry, I disagree. He isn't right at all.
Sure he may see that Madhu's seemingly moving on with another guy and even spending nights with him, but as other commenters pointed out, he gave her up. He "divorced" her. He has no rights over her.
Sure, he feels jealous because he unconsciously loves Madhu, but lets not forget, this was the guy who humiliated her. Who played with her entire life just to prove a point. Who almost emotionally destroyed her after everything she had done for him.
As of right now, Madhu is a free woman and she can do whatever she likes, even if that entails going out with some guy. RK has no right to say anything.
Anyways, on another note, I do hope the CV's redeem RK's character. I really do hope him and Madhu end up together, but only if he is redeemed.