Misunderstandings are fun, but this is a new kind of dense.
Its a little different than unusual denseness tho.
Protag actually managed to confess his feelings in the first chapter, but the heroine answered as "ookini" which is a kind way of rejecting / passing it in the general sense of japanese. She didnt meant that, but considering she doesnt wear the ring as well no wonder protag thinks that she doesnt like him / doesnt want to be fiance.
So now, Protag thinks that the heroine forces herself to spend time with him and obviously over-thinking every situtation, not want to be over pushy etc. TBH I'd say more than half issue lays with the heroine, protag did a very good confession just answer him in a proper way and its all gucci.
Basically imagine confessing to a girl and getting "OK" as an answer, and despite that dude is still trying to built a good relationship with her.