Complex sentence: Later, she accidentally found out that Raku and Kosaki has like each other since middle-school, and she ran away from home so both of them can be together, unaware that Raku also likes her.
Split into simpler sentences: Later, she accidentally found out that Raku and Kosaki had liked each other since middle-school. To help them get together she runs away from home, unaware that Raku also likes her.