I was between 7 & 12 when I read it, so 1980-85. Probably aimed at young adults. Set in a society that (I think) lived "off the ground" somehow. I have it in my head that they lived in elevated glass domes, which were either floating or on towers. The protagonist, perhaps narrator, is a young boy of a servant class/caste. He falls in love with a girl from the ruling class, and it ends with them escaping, I think in an old-fashioned hot-air balloon (the type with a basket).
My first question here; thanks.