Lewis wasn't able to have enough time to pay attention to this mini detail when he met Sol personally at the party in Ruben's restaurant that night - the fact that he's aware of him being someone who used to be more than a friend for Lillian, that is.
While they were exchanging looks, little did the Count's son know that this is the train of thoughts that's running in his mind at that moment.
It seems like Sol himself is still not aware of Lillian's feelings for him up until now. She had been crushing on him even way before she met Lewis before, and he knew that he's one of the reasons why she was crying near the patroness' monument during the first time he saw her.
Lewis used to be her living diary back then, after all. He's aware of almost everything about her that time.
