They've admitted/realized they're in love, but she's going to Tanglewood to follow her musical ambitions and he's going to MIT to follow his scientific ones so they're going to be separated and who knows if they'll ever reunite

I thought it was really not certain when I was very young and read the book shortly after it first came out (I read whatever Le Guin I could get my hands on then, which wasn't really that much). They're not what society would have called romantically involved then, at the end of the book.