Source: Himeno-chan ni Koi wa Mada Hayai ch. 39. Context: Lone guy at a girl's birthday party (he's her crush). Spoiler: Answer: {} That punchline got me good! Anyone else also thought "harem"?
They seem a bit too young, at that age boys and girls tend to be able to interact just fine with one another. It's only at the pre-teen age that they start splitting up usually.
Ah, yes. The good old girls only party but somehow I, a guy, was invited? Misunderstandings be damned!