Well, if there were any threats made verbally, you could try to record them secretly if it's legal in your area. Another way is to look for any patterns of behavior that led up to the blackmail. For example, if your friend had been making inappropriate remarks before the actual blackmail attempt. You should also document your own state of mind during that time, like if you were scared or felt forced. This can all be used to build your case.
Save any communication that shows the blackmail. If it was through text messages or emails, keep those as evidence. Also, if there were any witnesses to any part of the situation, get their contact information and statements.
This is a very serious situation. First, you should not give in to the blackmail. Immediately cut off contact with this so - called 'friend'. Then, you must report this to the police as soon as possible. They are trained to handle such cases and will protect your safety and rights.
First, you should support your wife and make sure she feels safe. Then, you need to confront your friend immediately. Tell him his behavior is unacceptable and illegal. If he doesn't stop, you should consider involving the police. Blackmail is a serious offense.
If there were any witnesses, get their statements as soon as possible. Their accounts can be very powerful evidence. Also, if there were any electronic communications related to this coercion, like text messages or emails, save them carefully.
You can start by writing down all the incidents as soon as possible, including the time, place, and what exactly was said or done. If there were any witnesses, try to get their contact information and statements.
To prove your doctor is stalking you, keep records of any unusual communications. For example, if they send you excessive texts or emails that are not related to medical treatment, save those. Also, if they show up at places where you are regularly, like your workplace or your favorite coffee shop, and there's no medical reason for it, note down the times and dates.
Proving it would be really tough. You'd need clear evidence like timelines. If your story was documented privately before Heard's, that could be something. Also, witnesses who knew your story first might help.
Telling your friend is going to be one of the hardest things you'll ever do. Be honest and straightforward. Choose a quiet and private time to talk to her. Maybe start by saying how sorry you are for the situation. Expect her to be shocked and possibly angry at first.
Open communication is key. Talk to your partner about your expectations in the relationship, including fidelity. Build a relationship based on trust and mutual respect.
She could seek legal help. If there is evidence of the blackmail, the law can protect her from such unjust treatment.
Just be honest and straightforward. Say something like 'I know you betrayed me and it really hurt me.' Keep your tone calm though.