
Shimakawa kisses Nemu bc he thought that Akira was still in contact w/ sanada-sensei (Akira's old teacher and lover.) Shimakawa's side and reason for kissing Nemu is here--->
http://www.mangago.zone/read-manga/hidoku_shinaide/tr/166388/page/

Didn't Maya already got jealous when Jutta was pursuing Nemu?
Of course the reason why Jutta wants Nemu is not so much romantic as Jutta actually wants to have what Maya wants (spoiled sibling/cousin mentality). But it still made Maya a lot jealous
And then of course, Maya was soooo jealous of Nemu's friendship with Okino at the beginning of college, so much so that Maya did the same as Nemu, that is, ask for a breakup. Only that they hugged in public and made a fujoshi blush :)
Did this Okino thing made Maya so jealous that he bought the pair ring to stake his claim?

well with Jutta it wasnt that much of jealousy since he knew nothing will happen he was only feeling possessive of Nemu since he hadnt said he loved Maya
and the Okino thing was just a one day deal not even a whole day more like hours
where he felt insecure not that much of a time
(omg how can i forget that fujoshi i thought it was a guy cosplaying as a girl lol)
yea who knows since sensei hasnt wrote anything about how that happened but that might have been one of the reasons for the ring
So Why did Shimakawa kiss Nemu???? I didnt catch that bit.
Also when will Nemu ever be Maya's equal? Right now Ruka is ok for Nemu but if there are other situations like this (like how Maya says he likes another guy although as a friend while theyre in bed) Nemu will surely be jealous and lose confidence again. Right now describing Nemu as boring would be going too far but its not exactly false if compared to Maya from an outsider's perspective. I just want Nemu to be popular enough to make him feel more confident. Right now he is not as confident as Maya even if it got better from before.