everyone is overcomplicating stuff, to begin with, agewise i'm pretty sure the boy is closer to her than his dad is
second, if you all think this is going somewhere you really are just dumb and have no understanding of media, this story is all about the love of the protagonist and the husband, they will just keep being lovely together, if you think they will give any relevance to this crush other than for a joke you really have a problem and should really start reading some books so you get some ammount of media literacy
third, you all are weird with stepfamily stuff, the girl is her stepmom,and he has keep his distance all this time, she is literally a stranger, being step-parents is the parental equivalent to being adopted, no relation at all, you don't see a cute girl, gets told by your parent "we are adopting her" and magically lose all interest because now you have a familiar relationship, thats not how it works and you all are so corrupted by dumb stepsibling porn that you all think being stepfamily means something when it doesn't, you all see childhood friends and think they must love each other and marry, but if the childhood friend mom marries the dad is magically wrong because they're step-siblings, even tought 10 seconds ago you all wanted them together
fourth, THIS ISN'T GOING ANYWHERE, i don't understand how this girl developed a crush on her a chapter ago and nobody said anything but now that the same happens to the child people want to drop the manga because they think that somehow the manga about the protagonist having a crush for older men might decide to suddenly date his younger step-son, like, have you even read one chapter of this manga? have you even read THIS chapter? the whole premise was that other people tought like that and both of them found it so stupidly impossible they couldn't take it seriously.
edit: i'm not changing the previous comment because i'm the kind that likes to double down and owns to what i say, but i do admit that it came out very rude now that i'm reading what i wrote, i guess i might have been having a bad day when i wrote it, the guy that said i was comming out as a douche is right, so sorry for being rude, but my points still stand, decided to add this edit instead of answering so this doesn't turn into a discussion in the comments