I Reincarnated For Nothing

who  is his other love interest? 

maybe the hero? iirc again chamber said there's only two. 

asmodeans  are corrupted humans. happened during power/mana research 

pretty much everyone in his party (females) given him at least one child. with minor some exceptions.
like hero, saint, dark elf, etc.  (those are not exceptions). 

What happens to the thief who killed MC introduced in latest chapter, how does MC screw him over? 

yes but there was other besides the golem 

Wait. What? 

there were no asmodeans originally. humans on their quest for power twisted mana into some stuff. humans after absorbing this stuff became asmodeans.