Camping here cuz i wanna know too :)
I won't say obsession, more like yearning.
Try Melting Point.
You find out later:
https://www.mangago.me/read-manga/special_benefits_for_newlyweds/
Also:
https://www.mangago.me/read-manga/the_last_step_on_the_way/
https://www.mangago.me/read-manga/ii_mon_waru_mon/
https://www.mangago.me/read-manga/dawn_of_the_dragon/
https://www.mangago.me/read-manga/escape_into_oblivion/
https://www.mangago.me/read-manga/hwang_young_s_misery/( bad ending)
https://www.mangago.me/read-manga/the_mansion_summoned_by_ghosts_cupid_scans/
https://www.mangago.me/read-manga/a_tree_without_roots/
Oh you said oblivious to it.
Then ignore everything I said and just these:
https://www.mangago.me/read-manga/special_benefits_for_newlyweds/ (they have. A past)
https://www.mangago.me/read-manga/love_plan/ (past)
https://www.mangago.me/read-manga/sugar_trap/
Can someone recommend me a BL where the top falls in love first and the bottom is oblivious to it and the top has to be like very obsessed more than the bottom