Mutual obsession bl?

https://www.mangago.me/read-manga/my_boyfriend_s_a_ticking_time_bomb/

https://www.mangago.me/read-manga/the_third_ending/

https://www.mangago.me/read-manga/makitakun_no_koiji_wo_jamasuru_to_shinu/

This is one of my favorites of all times because of that reason, but mind the horror tag (I'd call it vanilla horror tho, despite there's some gore) It's the one you'd say "they're absolute freaks about each other", literally https://www.mangago.me/read-manga/black_mirror/

And I adore Brothers without a tomorrow's works. I haven't read all of them, but Taming the tiger, Blood Link and Smyrna and Capri share this soulmatism between the characters that I love, and even though there might be some redflagish cliches at the early beginning, they're not overlooked