Responses
Actually the ML did say that he "didn't expect to fall in love with her" stating that he does indeed love her, and is just waiting for his sister to find happiness before he can because he still blames himself for what happened to sister.and yes it is a possibility for the ML to fall in love with another girl or lose interest in the FL. But luckily this is a manga and I doubt the author would want drag along the ship like that while trying to keep the attention of audience at the same time.so the most likely thing to happen is a sister realizing that she's just being a nuisance and try to be better ╮(￣▽￣)╭
if that love interest develops feelings for someone else? Then what? You've wasted a month, a year, maybe ten years in the friendzone waiting for someone to like you back and it never happens? Reika-chan would be much better off kissing those two nut-cases goodbye and going out with someone more normal, like Saotome, who actually likes her and wants to date her.