https://www.mangago.zone/read-manga/alter_ego_1/ (SEQUEL: https://www.mangago.zone/read-manga/alter_ego_2_noel_june/)
https://www.mangago.zone/read-manga/itd_would_be_great_if_you_didnt_exist/ (sort of)
https://www.mangago.zone/read-manga/two_birds_in_spring/ (MC has a boyfriend who used to be in a relationship with the FL, MC and FL don't really fight for him if I remember correctly but they do end up together; adultery)
Forgot to say that these are all GLs lol.
The side couple in
https://www.mangago.zone/read-manga/cherry_complex/
Owhh protect your purity and boundary of delusion
Bl, gl, with a love triangle, BUT the 2 competitors eventually start to develop feelings for each other or kiss. Like a rivals to lovers type of story.