He even sacrifices his own mother in order to help the daughter of a woman who wants him dead and a man who treats him like cattle, simply because she's the only person his own age who he can converse with.
Like he purposefully waits until after the little loli is raped before saving her, what, because he feels saving her is inconvenient? Then, when he finally does save her and turns her into his slave, instead of learning the other world's language himself, he goes out of his way to have the dungeon core teach the slave loli the language, all so he doesn't have to go through the effort to write for himself.
when he learns the loli slave was previously named "Meat" (a slang for s*x slave) by the former master, he makes no attempt to change it, even though he realizes the meaning. Of course, as expected, he's treated as a pedophile by every human character he meets, all for the sake of a "comedic" situation. Then when he receives his first adventurer request (cleaning toilets, wtf), the MC comes up with some convoluted lies in order to hide the fact he is good at magical toilet cleaning (who cares?) all so that he can have more "hilarious" misunderstandings? Moreover, not only does he go through so much effort to hide his "amazing (?) " abilities, but he makes it look like he left his loli slave to clean the toilets by herself while he played around on the town.
at least for the girl who betrayed him that seems to be false. Its just my conjecture from the author's foreshadowing, but it seems that the MC forgives the girl who betrayed him; moreover, it seems she somehow time travels into the past and saves his pathetic life (Vol 1, Ch 6 & side story Noriko's revenge). So not only does he not get to take his revenge, but he ends up indebted to her after she tries to kill him in the first place. In order to make this plot development feasible, the author tries to garner sympathy for the girl by showing that her life was crap after she betrayed the MC... that doesn't really help the story when the only thing the readers have to look forward to is the MC's revenge (that's the result of making the story so depressing, author-san).
to see the MC publicly humiliated, NTR'd, cut up limb from limb, spiral into depression, then get his revenge and sole reason for living taken away...