So this was a series of three books that were written as letters between two fictional characters (first one is their two names... just can't remember... ) who never met but grew closer in their correspondence. And these books were beautifully done--each page was a different "peek" into the letter (a kind of pop-up book for adults), so it was maybe an envelope with a folded note inside, for example. They were very popular, so I'm sure someone out there who hasn't burned more brain cells than me can remember the title of the series/first book..

Thanks.

I suspect you're thinking of Griffin & Sabine, Sabine's Notebook, and The Golden Mean by Nick Bantock.

That's it---thanks so much! Now I know what to tell my husband to get me for Christmas--ha ha...