Oh, I made a discovery about yet another Japanese currently airing series that's BL adjacent - meaning bisexual polyamorous storyline plus also starring two familiar faces from other JBLs: Iwase Yoji from "Takara no Vidro" (Be still my beating heart!) and Mashiko Atsuki from "Taikan Yohou".
It's "Kita-kun, Our Shared Love" (full title is one of those Japanese mouthfuls: "Kita-kun ga Kawai Sugite Te ni Amaru no de, 3 Nin de Share Suru Koto ni Shimashita" = "Kita-kun was so cute that we couldn't handle it, so the three of us decided to share him")
Although there's no official international release or English subtitles yet (as sadly often with J-dramas), there's a good fansubber. (Link can be found in MDL comments.)
Only one episode so far. I had planned to wait until all are out and fansubbed, just in case, but I couldn't resist, so I'm watching it now. Looks good!
ETA: Watched it. Loved it! This is now tentatively my favourite currently airing JBL (even though it's arguably not really a BL).