All this time, Mullai was sitting on the bed and witnessed all of this unfold.

She's angry that he didn't even wish her happy birthday.

Mullai: Yenga?? Inniki oru wish kooda pannala. Romba super nga, romba santhosam. Naa thaan oru muttal maathiri ring ellam vikkai poi ellam senjen. Aana neenga oru vazhthu kooda sollalala. Porantha naala keduthuputachula. Nalla irunga. Nalla santhoshama paduthu thoongunga

K turns around is simply shocked to see her in their room. 

He's confused and tries to stay calm, but he couldn't. The thought of her not wanting him and her accusing him of ruining her birthday forces him to have his first breakdown.

Kathir: Aama nee eppo inga vantha? 

Mullai: Naa varathu irukatum... neenga oru vaati aavathu enna nenaicheengala? oru vaati avathu enna inga kootitu varanumnu thonicha? SOLLUNGA

Kathir: Aama nee phone pannumbothu ellam thiteetu, ner la vanthu paakalamnu vantha appayum thieetu, ippo pesuva di pesuva

Mullai: Naa eppo? Neenga eppo ?