You guys, he's not dense! He's just got cripplingly low self-esteem!
Which isn't any better but still!
I feel like, as generally well-written as this is, this is an element that hasn't really been established as well as it really needs to be. It's clearly central to his personality and to explaining why despite these girls being INCREDIBLY obvious he is in actual denial over their feelings, yet it's never really been established in any major way EXCEPT for the fact that he's in denial.
I assume the idea is somewhat similar to my dress up darling. He's a dude who's effeminate and likes sewing, so he was treated as undesirable his whole life, which combined with his early period at this school just hammered it home.
That all said, I will say high school boys can be VERY dense. When I look back on high school I realize several girls were giving me very clear signs and I just couldn't fathom that they were doing anything other than teasing me. It's honestly funny now when I think back because it literally included straddling, and I just thought they thought it was funny to make me uncomfortable.