I also love that trope and I will be running to watch Misty right after I'm done writing this!!
https://mydramalist.com/29722-boyfriend perfect fit, but the hubby is 2nd ML.
https://mydramalist.com/32007-www 3 FL, One of them is in such a relationship.
https://mydramalist.com/31550-i-love-when-i-m-sad the husband is the only good thing about this drama. Such a great performance!
Missing you They're a live in couple, he's definitely more into her than she is into his and there is a dark obsession component. 2nd ML
https://mydramalist.com/25154-the-first-love-of-the-man-who-was-thousand-years-old fantasy elements. She doesn't remember him till the end, so even when she gets with him, she's a bit detached and he's all in. He's the ML.
My heat twinkle twinkle this fits perfectly. The drama is not the greatest out there, I just focused on the main couple and FFW the other characters.
Summer's desire they're a highschool couple but act like a married couple and he's obsessed but she's just going along. It goes darker from that.
https://mydramalist.com/16851-the-good-wife but really she's got good reason! He cheated on her.
https://mydramalist.com/22292-the-kings-woman it fits really well.
https://mydramalist.com/10130-wong-wien-hua-jai Thai drama. I feel like Thai drama have more of this
https://mydramalist.com/15090-i-have-a-lover here it's more the reverse. He's the one who doesn't feel it anymore in the beginning. But things happen and get a bit switched for a bit.
https://mydramalist.com/60609-unfamiliar-lover memory loss
https://mydramalist.com/714811-101-marriages I'm currently watching this because it's basically that exact trope. Not the best production though. I skip a lot.