Samenai Yume
I love this so much. It has elements of necrophilia (well, not entirely) and incest.
Brutal: Satsujin Kansatsukan no Kokuhaku
Camellia
This is so good HUHUHU. Unfortunately, the author dropped this. But based on the spoiler (since the author already said that this will have an unhappy ending), according to one of the comments below, the Father/Natsuki died and Hyou committed suicide HUHUHU, while Setsu became a lawyer, but he didn't end up with anyone. SHITTTTT, this is so sad.
Zankoku Na Kami Ga Shihai Suru
This manga is from the 90's, but I love the plot. The ending, I don't think it was happy or bad, just an ending to a moment, like in real life when stuff just ends or continues, kind of an open ending. To be honest, I don't ship Ian with Jeremy, but I love William, Marjorie, Valentine, Eric, and Poppy.
Boys Next Door
Hmm, this is a bit sad, but what I admire the most is Lawrence's beauty.
To the Sea