SOLVED. 2 short mystery books with a series of letters sent back and forth. [s]

[Edie]

I read these back in the early 2010's when I was like 8 or 9. There are two books in the series. Both are made up of letters sent back and forth between a man and a woman who are trying to meet up. The man travels around the world and keeps just missing the girl. I clearly remember how it ends but the group rules say no spoilers- should I post it? The ending is a big twist, and it ends mysteriously. I don't remember what happens in the sequel but I do know that it is also letters. One book was mostly red and one was mostly blue (I think the first was red and the second was blue). I've been trying to find these books for years- please help!

[Bryn]

Griffin and Sabine?

[Edie]

Aah yes, thank you!!

[Bryn]

You're welcome!

[Edie]

I'm on mobile and can't move the discussion- can a mod help?