Any stories where the male and female leads become lovers early on and there's some asshole who keeps trying to sabotage their relationship? Maybe at one point he succeeds and she either starts to date him or gets real close. She reconciles with the male lead in the end.

Boys On The Run is essentialy this (although in the first case it's not an established couple), but it's hard-boiled seinen, and something tells you're looking for something more subtle in shoujo/josei.
I think?.. there was something like that in Love Stalking!, but I'm not entirely sure, maybe I'm thinking about something else.
https://www.mangaupdates.com/series.html?id=22839