I don't know any Asian novels but I do know a few English ones. The Anatomy of Jane by Amelia lefay Love slave for two by Tymber Dalton It's from the female POV though....
hmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm its straight up easier if you just search porn tbh
Most threesome I've read is MFM, with the girl as the meat of the sandwich. The men rarely touch each other during sex. I think they are looking for stories with a man in the middle?
Daily Grind in royalroad has that kind of relationship (a guy who is in a relationship with two people, one is a girl, other a guy), but there wasn't much development between them due to other problems they are dealing with, though there might be more later.
so are you looking for love triangles or a threesome? can't say I've read many BL with a threesome, let alone one with a female welcomed as part of it.
Try looking for MMF https://www.amazon.com/s?k=mmf&ref=nb_sb_noss_2 Megan Derr's Lifesworn series has two such couples too.