Exactly as the title says. Getting really caught on how to write a detailed hedonsitic character who derives pleasure from ?kind of? immoral things; copious amounts of sex and drugs, killing etc. I have no idea how to write his desires or motives, or even what his desires and motives could be aside from the short term things that I mentioned. This is regardless of character past, background, or what is going on in the world. What are some motivations, that are not as general as "X goes with group Y because they are going to do things that he finds fun", that a character like this could have. If needed I will try to bring his past into it, but it doesnt feel right for him at the moment.
I would recomend you look into some True Crime around serial killers as many serial killers are motivated by hedonistic motivations, so much so, that Wikipedia sub-divides Hedonisitic Killers into three sub-categrories as it's one of the largest categories by motive.
This covers "Lust Killers" (kill as part of a perverse sexual gratification they feel, with Jeffery Dalmer (his case is not for feint of heart) and the Green River Killer being examples), Thrill Killers (killers who get pleasure from the thrill of killing, and who's pattern does not indicate any sexual desire. Real world cases can be found in Robert Hansen, Carl Watts, and possibly the Zodiac Killer, who though never caught, did communicate to police that he found killing to be far more thrilling than having sex) and comfort killers (killers whose motivation for killing is the direct financial benefit they stand to gain from their victim's murder. Real life examples include Dorothea Puente, who collected her victims Social Security checks, and H. H. Holmes, who benefitted from his victim's deaths through insurance and business deals). It should be pointed out that contract killers and hit men do not fall into the comfort killer as they are killing on behalf of a third party for a payment for the service.