You can try my novel if you're interested: https://m.webnovel.com/book/immortals-the-curse-of-samsara_14820688106802605
It's a male lead story with over around 200 chapters + side stories in the form of chapters. Although it is a harem but, not like most novels where they infinitely expand, there's only 4 harem members and it's not like he's with all of them at the same time (ex: one of them is a former lover). They each also represent an aspect of his desires: lust, passion, etc.
Regarding the MC, he was born as a child soldier and grew up to be a mercenary, so he's definitely not a goody two shoes hero. And he's emotionally stunted, hence the messy relationships. And I can also guarantee that most characters are well developed, even if their side characters or love interests. It's one of the things readers appreciated
Edit: Right, also, it's 18+ because of gratuitous violence and described uhh .... love scenes. Ahem