Shit you mean the type of manipulative Yan ml I once imagined actually exists in a series? Damn imma go read that-
Also camping for more
Right off the bat, the first thing I think of is 'Color Recipe', but I dunno if thats what your looking for...
https://www.mangago.zone/read-manga/imitation_mate/
https://www.mangago.zone/read-manga/akuma_chan_wa_momoiro/ (this does have a lil "love triangle" but like it's too manipulate the MC, they have a deal of sorts)
https://www.mangago.zone/read-manga/iyayo_iyayo_mo/mi/597a0d16704b07363c6222c0d7bf087d_chapter-6/1/ (it's also hinted that the Top killed the girl who MC almost slept with)
Check out this list for this type of description you will come across the ones you are looking for -
https://www.mangago.zone/home/mangalist/1694666/
I'm looking for something like Ibara no Naka no Hana, where ML is a yandere—not the weak possessive type, but a real manipulative yandere. Even better if, even until the end of the story, the MC never learns about the seme's true nature. It's fine if the MC is sort of suspicious of the ML and finds out a little bit, but it's just the tip of the iceberg—white lies to hide even bigger lies. PLEASE, NO HAREM OR LOVE TRIANGLE. I HATE THEM.