
So this is my opinion but I think he knew she was his stepsister, saw an opportunity and took it when she pretended to be somebody else...because he has been in love with her..pushing her away all those year and sleeping with numerous girls to take his mind of his love for her all the while staying close..i.e. going to the same university..the only reason he moved out was so he could spend alone time with her where they could take their relationship to the next lvl..and he hid her from her friend not from jealousy but bc he knew she might of have been recognized..sooner or later, this is going to blow up..and when it does, I am ready and waiting to read that chapter..and figure out if my theory was right
ヾ(❀╹◡╹)ノ~

If we go along with that theory, for that thing about Tooru when he cried, I'd interpret it as him understanding that Minato finally doesn't want anything to do with him romantically, even if it's just pretending. In other words, he just loses all hope for them to be together, because if they can't be together when she's "Mina", then being together as "Minato" is all the more impossible, so Tooru cries, understanding the silent/implied rejection. Therefore, when "Mina" comes back, he has a renewed hope. Well, at least, that's what I think! ╮(^▽^)╭
For as many lame female MC's, I love this one, she reminds me of myself..I wish this was not a oneshot.. Σ(っ°Д °;)っ