His insults are out of anger on his part. And what did guddan think was going to happen when she went to his house? that he'd greet her with hugs and roses? She's not some beechari anymore. She chose put herself in that fire. Aj's state is anger 100% of the time, its not just directed at guddan. Does he need to repent for what he's done? yes he does and i'm not even saying what he's doing to her here in the party is right either, its not but if you look at it objectively, Aj's lashing out at her out of hurt nothing more. And love doesn't go away just because the other person hurt you. Guddan did what she was supposed to do, she left and made a name for herself. They both still love each other deeply and each in their mind is justified, as truth hasn't come out.
But again as far as guddan deserving "insult" in this party? she brought that on herself by agreeing to go.