
Also, don’t forget how shima views friendship as being a higher priority than love. So when they broke up, they returned to being friends, and since friends are higher priority than a lover, he didn’t feel as heartbroken about that. However, now he’s feeling conflicted since he’s realizing he does want to be something more than friends with Mitsumi, but that clashes with what he thought his priorities were. And that’s also why it took him so long to figure out that the feelings he had for mitsumi wasn’t friendship but love. Since the highest form of love he knew was friendship.

I really like how the manga is taking is time and showing how not being there mentally and the normal immaturity of people at that age can make you be confused about your feelings, Shima likes Mitsumi, isn't a shojo manga love, he liked her as a person first, and he is slowly learning the differences between liking someone as a friend, respect them as people, and eventually, with the right push, maybe something else in the future.
I cant understand how shima sees mitsumi.... like what does he feel about here? Does he really like her or just feel safe around her?