I wonder if the little sister loves the MC, too, and she miscategorizes it like her older sister does. Both love him...one thinks she wants to be his mother while the other thinks she wants to be his little sister. Also, childhood friend shouldn't be mad...she's the "mother", remember? It should be her job to treat her "son" to some cake, not the other way around. This is where her peculiarity has backfired on her...