Alex left after making sure that his sister had already fallen asleep. Today was an exhausting day for Belle. He knows that she doesn't have classes today. Belle gave him her schedule. But he knows that Belle didn't spend the day at her apartment or the studio. He has someone following her everywhere she goes.
He knows that Belle is aware that he has someone following and watching over her but surprisingly, his sister is not confronting him about that. Probably Belle knows that he was just doing that to make sure that she is safe, seeing that she won't let him help her in her dangerous escapades.
Today, Belle was all over the city and finally found out where her next target was hiding. And he was sure that she would not waste time visiting her next victim.
She will surely act as soon as possible despite him telling her to lay low and put it off for the meantime while he is chasing Arthur Brown away.
