Yeah, that look that was exchanged between the step-mom and Tomo-san was interesting. Also, on page 16 when Tomo accidentally hugged Ai-chan, she said "Huh, my mistake." I think it means that she had wanted to hug someone close to her subconsciously, and to me the most likely person would have been the step-mom since she was surprised Ai-chan was there. This could have all been my speculation, and that I'm reading into it too much.