I've got the letters my dad wrote to my mum both when he was overseas on national service, and when he was working away in the UK. She was married to her first husband with a daughter at the time - though I think the letters do go past this date (they are mostly undated, so have to work it out from context).
It's actually quite unpleasant to read. He was obsessed with her, in quite an unhealthy way. A lot of the letters talk about his vision of their future together. They mention my sister, which is quite sad because he was in fact very abusive to her after they married. But he was sucking up to this young mother (mum would only have been 20-21, he was three years older) through her daughter.
They also show signs of his controlling nature and say things like "make sure you eat something my darling, but not just biscuits because you don't want to get fat".
I don't think I have read them all. I actually first found and read them as a teenager at home, but now they are both dead I have them, though for now they are still in the unsold house. My sister wanted to have some ceremonial burning of them, but I can't be arsed with that - we either keep them or throw them away (I mean, she can do that if she wants, but I won't be there). My brother hasn't mentioned them though I left them in the "memories box" I put together of things I thought both of them might want to look through or take.
There are no replies from her. I imagine in the main she had nowhere to send a reply, but I think from his letters it looks like she did reply to some, but he obviously didn't keep those.