I know that. I understand their reasonings. I just asked why do a lot of manga protagonists as dense as this? Especially when most of them doesn't have such reasons for their dense-ness.
In his defense, everything "was" misunderstanding.
he simply asked for sex favor when he's snapped. He just want some information while he was unconscious and nope out after got all informaton from her but mitsuki was deperate enough to accepted it. so he changed his plan and move his base from his own apartment with 2nd best girl to shopping mall. that make him indirectly helped her more than enough since it's already his base.
He afraid that he might be virus carrier and his fluid might infected her. so he stayed by her side while she was sick. just to make sure if his theory was right or wrong. she thought he was "that" worried about her.
then they bonded during sheltering in the shopping mall for quite sometime, to the point that he blamed himself for not giving her a gun, make everything fall aparts during creepy guy attacked. (which he didn't notice it himself that he already trusted her to consider giving her a gun at that point)
after the "creepy guy" incident, their relationship is already at stage of "almost progress to next step) if they got time to sort it out but Ak-kun(blondie childhood friend) intervened before they got that chance. so they seperated with more "misunderstanding" (silly troupe, I know)
and in her defense, She feels like never truly give him anything in return except from sex favors. so she feel inferior to doctor hence dragging out the plot more.
The others manga are usually inferior complex trait MC in overpowered isekai/romcom plot where normal MC somehow having unique talent that won't be use anywhere except cover FMC weakness.