To end up cleaning for you with 〜ことになる

Grammar Explanation: To end up being with 〜ことになる

Urushi and Ayumu give their makeshift clubroom a cleaning to welcome potential new members. Considering that Urushi was the only club member before he joined, Ayumu remarks how she alone had cleaned the room for his sake last year.

うるし:: 「まぁ　結局(けっきょく)」; “Well, in the end...”; 「お前(まえ)しか入部(にゅうぶ)してないからそういうことになるか」; “You were the only new member, so it ended up as you say, huh?”; Literal: “Since only you joined, it becomes that kind of thing, huh?”

Key Points

1そういうことになる means it ends up that way

〜ことになる describes a result or arrangement that follows from the situation.
Here Urushi realizes Ayumu’s description is effectively true because he was the only new member.

2そういう points back to Ayumu’s interpretation

そういう means “that kind of” or “like that”, referring to what was just said.
The phrase avoids repeating the whole idea that Urushi cleaned the room for Ayumu.

3お前(まえ)しか入部(にゅうぶ)してないから gives the cause

しか with a negative verb means “only”.
Because only Ayumu joined, Urushi accepts that the cleaning can be framed as having been for him.

4か marks reluctant realization

The ending か is not asking someone else for information here.
It sounds like Urushi arriving at the conclusion herself.