Dreaming Back to Immortal Lord's Youth

[Quick time travel, two male protagonists, including BL, GB, no fixed CP, main line BE, there is a high probability that each main character will have a personal ending. There is no situation where Xiao Tan ruthlessly reveals the truth in the whole text. Maybe he will fall in love but he will end it instantly. Highlight! Teacher Xiao Tan will not be with anyone. He really cultivates the ruthless way. It is not the evil way of killing people to achieve enlightenment, but the serious ruthless way. There will be many vulgar scenes, but most of them are the pain caused by emotions. Teacher Xiao Tan will not fall in love with anyone, including himself. The only protagonist in the whole text is Si Tan, that's all. Being close to you means being close to pain, being far away from you means being far away from happiness, so I stay far away.