Unfortunately I have to agree here. I will never fully understand the "I don't understand my own feelings" trope.
I'll be generous and say you can occasionally get away with it (sparingly) but our guy is beyond dense, he acts like he is pre-pre-pubescent and does not, in fact, have even a conceptual-level understanding of romance let alone physical attraction. For her to make ultimately make a pass at him feels ... questionable ... now, because hey - you can't consent to something you can't comprehend.
I like slow-burn romances, I like the "awakening to your childhood friend" trope, and there's a lot I like about this manga but I'm going to injure my eyeballs if I roll them any harder. Hopefully the author will exhaust/resolve this situation so that they can move on to something more original. You know, like having one of the MCs get told they have to move to France or something, so that we can have a dozen chapters of "I can't confess to you now because it would break your heart."