I'm trying to find a yaoi which I've read long ago. I think it was a longer yaoi, I remember the extra chapter.
Uke and seme finally are together, they are really happy. But one of them died and the other became really depressed, he just drinks all day and hallucinating that his loved one is still alive. He is speaking with his spirit. It's really heart-wracking chapter which makes you cry. But at the end

he wakes up crying, and it was all a dream. And his loved one is still alive, sleeping next to him

The manga is not tragedy, I think it's more like romance or comedy. Uke and Seme have to take a long way to be together and when you finally think now everything is fine now, then here comes this chapter like it slaps you in the face.

I hope somebody is remember this manga, it's a popular one.

It should be Shachou to Hisho, Ai no Shoumei

Yes, that's it! Thank you!! 😀