Ruka is innocent!!! He did nothing! You guys can never see that Maya AND NEMU are the faults of their own break up. Do not blame it on Innocent Ruka!!!!
Ruka is, in fact, the one who started stirring up things between them, leading to their cooling off and other misunderstandings. He's told Nemu he plans to take Maya away from him, made Maya stay with him and relied on him excessively despite knowing that Maya has a boyfriend. So yeah, I dislike him a lot for causing so much misunderstanding.
He wanted to be friends with Maya, that was fine, but he wanted to monopolize Maya simply because he saw Maya had the potential to fulfill the things he couldn't do himself (because of his asthma).
There's a fine line between wanting to be friends and getting in between a relationship where his input was not needed. Even if Nemu and Maya had issues, those were issues the both of them needed to get through together privately, but Ruka went did a lot of things that strained them even more.
He bout to risk it all