believe in what ? If not like she in any position to betray anything to begin with.
She can have a fatass boyfriend. Who also may be old as her farther. And it still her own business
What's with some people getting triggered with a certain scene in this chapter? His belief in her could also mean he believes she's not involved in anything shady. Which I bet said belief will be tested if/when Kouta gets introduced to Sotomura.