Just let you guys know from what I read and tried to translate there is not chapter where he thinks she has a boyfriend or she mentions something about having one, in fact when he was ignoring her because he felt he could not be around her because of the comments of her friends, she told that they were already friends and then she says joking " then do you want to go out with me" so in my opinion there's nothing about a boyfriend I don't know where you guys got that from.