Basically, he achieved financial, professional, and social success at a very young age. It's a full-time job just to maintain his status - it'd be easy for him to become LESS successful, even through some minor social slip, but there's not really any room for him to go any higher, socially or professionally. He's not even 30 years old, and his life can only go downhill.
So he's trapped, disillusioned, he has no dreams or ambitions or hope for the future, he got everything he thought he wanted and he's still fucking miserable and alone. He's just getting angrier and angrier, there's nobody in his life he can relate to or talk to honestly. And he realizes that, if you're rich and handsome and socially well-connected, women (and other people) will let you get away with pretty much anything if they think they'll get something out of being closer to you.
He takes full advantage of that and, pretty shortly, gets bored of sex just as he's gotten bored of everything else. His kinks and preferences get more and more cruel and abusive until he's just outright torturing, mutilating, and murdering women. Then he's just lashing out at random strangers on the street.
By the end of the book (movie) it seems that he's completely unable to distinguish his fantasies from reality, and he's desperate to get caught, to get punished, to get some kind of acknowledgment that his actions have consequences and he's not literally living in a video game, or stuck in a coma-hallucination, or something.
But nobody gives a fuck. If Bateman really is killing people, they'd rather just not know about it. As long as he keeps showing up to work, showing up to social functions, and making money, they'd literally let him get away with murder. And that's his Hell, basically. He will never even know what he fantasized, or what he really did, because the entire city is mutually invested in covering up his wrongdoings so he can continue doing whatever the fuck he does in his fancy office.