Does the deceased know the truth about what was lied about concerning him after his death?

We have no knowledge that the deceased knows matters that were hidden from him during his lifetime. There is no reliable textual evidence to confirm the deceased's awareness of his family's affairs in this world. The important thing is to repent to Allah if you have lied, for repentance erases what came before it. Moreover, illicit relationships between young men and women are an abomination that must be repented from and one's self reformed.