I think that Youjun-sama did it for many reasons. He knew that as long as he had that power and was still alive, his clan would always be threatened. But if he were given to another clan (sorry, I don't know what they actually are), then that clan would overthrow his clan using his dreams. Also, yes, he loved Toutchirou. He foresaw that they would be together before he died. But Youjun wanted to leave the world like that. His wish was to be with his lover in his last moments of life so that his clan isn't threatened by his dreams nor will any other clan be able to use him. And dying was his will. He didn't stop it because he thought it was for the best.
They're dead meat.