He suffered major trauma and has incredibly low self esteem, which has been furthered by his uncle pimping him out.
He's not realising out of stupidity, rather due to a feeling of not being worthy. No one beside the ML since his parents died has been kind, cared or backed him up.
...to expect more from him to me suggests you're not acknowledging this pr aware of just how deeply trauma can effect how a person sees the world.
I dunno if you read this with your eyes closed or your brain turned off and while the web novel doesn't really go in depth on his use past relationship trauma it's SO easy to tell that hes being cautious because his past relationship has proven time and time again that things are never what he believes they are, he always goes into relationships with the idea of marriage but jes partner is never the same and they always take advantage of him so it's obvious after this happening to him so many times he wouldn't take the actions of the seme seriously until the semester himself says he's the one he wants to be with and reassure him
The uke is so stupid like bro the seme already introduced his parents and he still thinks they're sex partners