It's about how a pretty well adjusted man is perfectly avaliable, selfless, well adjusted and wiliing to wait for the girl's every whim as soon as they meet for some reason even though its perfectly reasonable for him to just go fuck that and move on. Specially in this case since Ban is not exactly a catch or warrants this degree of devotion.
I said i'm not suprised since female authors tend to right the perfect man and self insert as the female lead (like My Dress Up Darling). Exactly the same thing with harem MCs which is a genre i also hate with a passion.
Don't let your prejudice get in the way. This has nothing to do with the mangaka being a woman.
Yuuki is
not a well adjusted man. He still lived with his parents as a 35-year old. He had difficulties adjusting to
any relationship due to him not having any confidence in relation to his own personality - a fact that has already been addressed on chapters 5 and 6. He has, time and time again, at the start of the story, shown that he had absolute no confidence on himself when dealing with the opposite sex, to the point that he would not take any risks at all - leading to him being seen as uninterested and putting off any prospects.
Yuuki is not immature - he is a 35-year adult, after all. He may be inexperienced when it comes to romance, but he
knows the world doesn't end when things don't work out. Mainly because he kind of have had already lost any hope on that department before meeting Ban.
It was Ban that pushed him to accept a bit more whom he is (again, chapters 5 and 6). For him, Ban
is certainly a catch, since she seems to be a woman who actually understands his issues and supports him. Not only that, it's someone who actually sees his qualities, not only his faults.
You are portraying as if Yuuki's behaviour was abnormal - whilst in fact his behaviour is healthy. What is not healthy is to throw everything up in the air because of something that might as well be a misunderstanding.
Ban made a mistake, she noticed she has such a mistake and tried to make amends. Yuuki is mature enough to recognise that and to notice what really matters.
You talk as if he has seen her leaving a love hotel with Asal. She went to grab a meal with someone with whom she shares a past - a painful one at that - and is now having to live at the same place. Of course Ban would have to deal with Asal sooner or later. Not only that, Ban will have to also deal with what went on between her and Asal - which is the cause of all her confusion about her feelings.
I believe it's a mistake and, quite frankly, a bit naive to believe it's just easy and "right" to say "fuck that" and move on when in a situation like that. Yuuki is
head over heels for Ban. He doesn't just fancy her, he's actually in love with her - and with good reason, as shown until now with how she treats and supports him. Why would he walk away from that without
actually knowing what's going on?
Apologies for the long comment here, but in my view it's just prejudice to put this up on the mangaka being female. It's just good, adult writing. This isn't a simple high school romance. It's a messy story between two people on their mid-thirties, with all the luggage that brings.