^That day^ is the DayOfTheLord Jesus Christ.
The FallingAway will happen as a result of -> false teaching leading to false expectations -> deceitfulness of sin and its legitimization -> turning from the Word and fellowship in the HolySpirit .
The ^man of sin^ is the beast, the antichrist.
The revelation of the beast is accompanied by -> a complete disavowal of sin -> denial of Jesus Christ -> glorification of humanity.