I have the same strained problem with my BIL. He wisked my sister 3000 miles away and now everything seems like a negotiation to keep it that way.
He takes a standpoint that I can work and it puts me on the defensive stand and keeps me explaining myself.
I’m expressive and it puts me at a disadvantage to him. He’s like gathering info all the time… i make adult conversation that has meaning and he dodges by talking more to, and about his kids.
He’s in medicine but doesn’t appreciate the mental side of health. I could go on and on…
If you think he would be receptive to anything in the letter, go ahead and write one. But if you think he would just mock you for it, and make you feel even worse, don’t. Some people are open and receptive to honest, respectful conversations about feelings. Some people aren’t. It’s not always worth it to open yourself up to people if they’ve already shown themselves to be the kind of people who don’t care about your feelings.
If you do write a letter, try not to insult him or blame him for things. Instead, focus on how his actions have made you feel, and how you think you can both work to make your relationship better. If you just want to write a nasty letter yelling at him for acting like a jerk, that will only make things worse and possibly get your whole family mad at you.