So much hate on both sides... The manga is not finished yet and, as things are now, it seems like Masamune feels better with Yoshino. He wasn't that interested in Aki, he's only purpose was to get revenge on her which turn out to be useless and started dating her because of a misunderstanding. He had only clashes with Aki till late in the manga, while it was a slow, behind the scenes, development with his master, not too well described hought. So, as happens in reality too, you feel better with the boy/girl closer to you, so the ending with Yoshino makes sense. I dont' know if in another chapter the author can pull an Aki turn and end with a Masa x Aki. But this hate is not justified, read the manga again and you'll see that they had/ have a lot of issues. What a long poem...