WTF? Tomo and Ibuki have been inseparable since they were kids, how did their parents completely avoid contact all these years?
The story started in their first year of high school, four years after the titular promise was made, which Chapter 1 establishes as basically the start of their friendship, for which Chapter 2 frames their typical proximity as being in neighboring classes the whole time.
Tomo implicitly hadn't invited Ibuki over to his house before
the end of Chapter 11. Chapter 12 establishes that she hadn't met any of his siblings or his mother, and his mother had only known of her by Tomo's accounts before that visit; he briefly spoke to Ibuki's mother on the phone before that, and from the looks of it Ibuki's mom is a working single parent with no other children.
Not everybody brings their school friends over to their house between the ages of 12 and 16. Add to this Ibuki having had two different isolating gender-performance dynamics in that time, and it's unlikely for her to have had
any friends over to her house while her mom was home in that time.