Nifrea just wants Ainz to help Ainz's love life. Since Ainz is surrounded by hot babes at all times and everybody wants his dick, even if they are a man or a heteromorph. Just how much of a sexual tyrannosaur does one have to be to attract literally everybody without even having a dick?! Nifrea rightly understands this, because even he is attracted to Ainz, if even a little, so he wants to help his master out. It probably doesn't occur to Nifrea that Ainz doesn't care about sex, because humans like to give human traits to nonhumans. It's a like leaving offerings for gods: the lowly human believes the gods to be like himself, and offers them something that he believes the gods will enjoy, not even thinking that the gods might not care.