I've just watched an episode of the crown were Princess Margaret and Peter Townshend wrote letters during their romance. I'm relatively young but during the late eighties and early nineties in my teens when I was discovering girls and dating I used to always write, and receive letters from the girls I was seeing. They were a mix of soppy teenage pap, highly sexual imaginations of things we were going to do to each other and heartfelt confessions of undying love.
This was before the Internet and everything it entails and was a remedy to not it being able to say the words face to face. I suspect the kids don't write letters anymore but surely I wasn't the only one who did this.