This has bugged me for years—posted about it on Library Thing back in 2018 (link: https://www.librarything.com/topic/292966#6515048) with no solves, but adding more details now in case it clicks for someone.

I read this book in England in the late 1970s/early 1980s (probably on a shared bookshelf at my dad’s work—likely a US import or British edition). It was a quirky/strange YA (young adult) book, from a boy’s perspective, more mystery/adventure with family secrets than straight romance (though maybe light romantic elements or betrothal tension).

Key bits I remember:

• Two children (boy protagonist + girl) who were either betrothed young, arranged to marry early, or possibly cousins (that part’s fuzzy/weak).
• Strange adventures happen to them.
• Possible gypsy/Romani/traveler family background (one or both sides—maybe adding outsider secrets, wandering, or cultural quirks).
• The story builds to a climax/reunion near the end: They find each other again at the Kentucky Derby (or a Derby-related event). He spots her in the crowd (possibly amid race horns or excitement), she’s wearing a polka dot dress, and “My Old Kentucky Home” is playing (or tied to the scene somehow).
• Not primarily a romance; more YA adventure/mystery with a poignant, symbolic ending.

No idea on title/author/cover—it’s obscure, maybe small-press or regional. Anything ring a bell? Even partial matches or similar books would help!

Thanks in advance—it’s one of those that pops into my head every few years.