Suggest me a book with a similar romance to The Doctor & River Song

So I really love the idea of a book that has a backwards romance like the Doctor and river in doctor who – something heartbreaking where as one person falls in love more the other person knows them less and less. The issue here is I don’t want the curious case of Benjamin button, I want something fun and whimsical where there’s more to their story than just the opposite timeline.

I truly don’t know if this exists, so any suggestions of anything similar would be wonderful!

Many thanks!!