I wonder if he means it because he never acts that way with Kuhu lol. He never seems insecure of his position in her life. I wish we got to see that side more. This dialogue comes off as just some writer not getting the Kunal memo because it's not consistent with his actions.
I disagree here. He has been rejected quite a few times now and that has always happened after he became serious about the relationship. So he fears being rejected again. Trying to be all confident and aloof works like a defence mechanism so that if and when the anticipated rejection hits, he doesn't feel like he gave it all and still got rejected. He has become so used to it that he doesn't realise that he is doing it. His mind hasn't realised that he will lose here if he keeps this up.