Throughout the manga, she talked about not feeling real attraction to the guys she was dating. The mangaka portrayed her as a lesbian who was dating men to appear cis. She never spoke about being attracted to both boys and girls. She strictly talked about having strong feelings for her female friend and no one else.
If the author wanted to portray her as bi he/she should've done a better job in doing so. Instead of making it seem like Masumi broke up with her bf's because she wasn't into boys, they should've put more emphasis on the fact that she didn't want to date them because she was in love with her female friend (forgot her name).
That ending was TRASH! Masumi deserved better and making Touma and Taichi a couple, in the end, was not called for. I want my damn time back. WHERE WAS THE LESBIAN REPRESENTATION???? I'M SO PISSED.