I read this years and years ago so the only details I’m pretty sure about are:

• it was a one shot
• it was published before 2007
• the seme and uke grew up together
• the uke has long dark hair
• there was some supernatural element to it, the uke wasn’t fully human but I can’t remember what his other form was
• it had a sad ending, one of the last panels was of them having sex and the uke thinking to himself they couldn’t stay together

These details are pretty fuzzy which is really annoying bc they’re pretty important:

• I think the uke had shorter hair when they were younger
• they couldn’t stay together because the uke was dying or disappearing or something like that. It had to do with his other form, really wish I could remember this detail I feel like it would really help!
• I think it had a historical setting but don’t quote me

Thanks for reading! Hopefully someone recognizes this, it’s been haunting me for years🥺

probably not right, but wanted to give it a shot with some oldies, granted most of these I haven't read/seen in like forever

Zetsuai (1989) or the sequel Bronze (1992)

Hyakujitsu no Bara (2005)

Ai no Kusabi (anime from 1992)

Ah sorry it was a one shot! I’ll add that to the post body to make it more clear. I don’t think it was that old necessarily, the art looked decently modern. Thank you for giving it a try!

Probably not the one you’re looking for but similarities remind me of Osananajimi ga Kamisama datta Hanashi so you might enjoy it.