Has anyone ever witnessed this? If so, how do you deal with the situation when it's happening to someone you care about?
The spirit of Jezebel is not necessarily a demonic spirit, but an attitude of mind, or a serious character flaw which resembles the ways of the immoral, wicked, evil and idolatrous women called *Jezebel* in Scripture. You could include Delilah in this mix, who was ruthless enough to destroy Samson, while pretending to love him.
(Of course, Samson should never have been foolish enough to get involved with this heathen woman in the first place, and that would also apply to your friend).
You could even assume that a demon is behind this kind of evil and controlling *Jezebel* and seeks to do harm to your friend. We will never know how many evil people are actually controlled or even possessed by demons, but sometimes it becomes completely obvious.
If someone you care about is being manipulated and used, but is close enough to you,
you can provide spiritual counsel with prayer (and even fasting if necessary). If that person has not been saved and been born again, they will not have the spiritual ability to resist Satan, and the lusts listed in Scripture. That can only come by the power of the indwelling Holy Spirit.
So that is their first priority, and Scripture must be used appropriately. And in order to do so they will need to repent of their obsession, and turn away completely from this person who has literally become an idol.
Without repentance there cannot be remission of sins or deliverance from bondage or demons.
At the same time,
Christians will need to be praying for this person, that the Lord will open his eyes to the reality of what is happening, and give that person the spiritual and moral strength to walk away from this situation totally.
Unless a person is willing to make a clean break from evildoers, they will always be in control.