I think I'll drop reading this manga here.
Not because it's bad, not because the art is bad, or not because the story is bad either per-se.
I just don't like the way this plot revolves around the fact that the dad is dead, and this situation is the product of that fact.
I don't think this is a sad manga, but I don't think it's a happy one either. I just get this constant feel of melancholy when reading this.
(and that I don't really like, since I like to prioritize content which uplifts my mood/emotions in a positive way)
I think if this was a hentai, even that would have a happier ending/plot (though in a twisted way, but still), since it would be obvious for the son to end up completely (or at least almost) replacing the father's place in the mom's heart (and in her bed also).
These are the types of characters to whom you hope all the best for, and for them to not ever be sad/melancholic/depressed again, even though a dear family member have died on them in the past.
I hope this manga at least has a happy ending with a good closure.
(I think that would be something like the mom re-marrying (since she's the kind of person you won't ever want to live alone/be lonely), and finding a new love into her life (u know, a good and a chill kind of a guy who the son would approve of), and someone to save her from the spiders, when the son moves away eventually.
Then the son marries the manga-club girl, and they all would move to live in a huge, ancient style japanese house, and the mom & his new wife would both draw manga and make a steady living for them-selves...)
That would be the best ending that I can come up in a few minutes (since I don't think we'll get the hentai route anyway)