in case of raj it is fully justified.
she believed raj to be perfect, brave, truthful.she trusted him the most. she had even asked him the reason for him being kind to her during the dance sequence. somehow she knew he was hiding something. that shows raj is kamzor. he did not have the courage to tell her the truth in the very beginning. he lied to her. he has cheated naina. and naina being naina did exactly what she was supposed to.