Unrequited love

MC is a master who adopted a disciple who is madly in love with him. However he does not acknowledge his feelings which causes the ML to become possessed by the demon lord

FL yearns for the love of her fiance but he fell in love with her sick sister. She goes through hell and dies but always comes back seeming more insane each time.

Very depressing
Side omega overdoses trying to win the ML but fails as he mated his childhood friend. He deteriorated and it is a hopeful ending