I wonder if it was unusual for Holly's boyfriend to spend the night?
Or if he spent the night often, but left before the phone calls that Holly and
her mom were known to have had.
The reason why I wonder if it was unusual for her boyfriend to spend the night,
is that the mom thought that Holly was sleeping due to a cold, and that was a reason why she thought she did not answer the phone. Does that also mean that Holly's mom was not aware that Holly would take her son to the bus stop, or perhaps Holly's mom figured she would go back to sleep after she arrived home from taking her son to the bus stop?
I think with not enough information, these questions linger and take on a life of their own, questions that raise more questions.
IMOO.