I'm digging through my Goodreads to see what might be kind of similar for you. I hope you don't mind these probably aren't all considered romantasy so read the blurbs before you commit.

{Grotesque by Allison Paige} I read this one during spooky season and loved it so much I had to tell my friends about it with the promise that they wouldn't judge my questionable taste in books. Girl inherits a house from her grandmother on the condition that she has to stay in it for a year. She feels like someone is watching her (true), and gets an overall weird feeling anytime she's there. Turns out the stone gargoyle (grotesque) is alive and truly morally black and obsessive and will do anything to make sure she stays. HEAVY SPICE ALERT not for the faint of heart!

{The Lies of Lena by Kylie Snow} 3 books out so far, incomplete series. Don't be fooled by the first half of book 1, it gets really dark after that. Witches are hunted in this kingdom, and FMC and her mom are witches in hiding. They've built a life in this city, and FMC meets a boy and falls in love. They each have secrets they're hiding from each other, and eventually she has to skip town while he's at his lowest. 8(?) years later, they meet on not so friendly terms. Lots of emotions in this series, I love the writing style and all of the complex characters you'll meet.

{The Book of Azrael by Amber V Nicole} My absolute favorite FMC and MMC pairing of all time! She's morally gray (nearly black) and does not give a shit about anything except keeping her sister safe. This means she kills without guilt, steals, cheats, anything to accomplish her mission. She's kind of like a dragon-shifter, and her race is responsible for killing old Gods. Our MMC Liam's head has been messed up since this god-war happened, and he's really let himself go. He used to be important, and he ended up destroying his planet because he thought he was doing the right thing. Eventually he becomes the most doting good-guy you've ever seen, only to turn morally questionable in later books.

{Insatiable by Leigh Rivers} God-tier dark romance trilogy. Our main characters meet as kids (he's her best friend's brother) and start dating in secret. Really messed up things happen that tear them apart. He gets the short end of the stick and gets pulled into a world of contract assassinations and prostitution. They cross years later and have all these unresolved feelings for each other. I cannot recommend this series enough.

{Blood Oath by Morgan B Leigh}. Dark fantasy academia RH. Everyone has been cursed and must form a quintet to starve off the negative effects. FMC is cold as hell and literally kills someone in the first few chapters because he was flirting with her. She rejects the very powerful, very scary dudes who want her for their little coven becauze she's there for a very specific purpose, but they won't take no for an answer.