I was really young when I first saw this movie.. all I can remember is a fairy princess who falls in love with a human boy but this is forbidden and in the end I'm pretty sure he dies.. also something to do with a crystal.. cartoon/anime.. Really wish I could watch this again.. any idea what it could be? It was recorded on this tape that also had lady and the tramp and watership down on it.. don't know if that helps any..

Young fairy couple in a forbidden love
Affair

There was a Romeo And Juliet style romance
In

The Sea Prince and
the Fire Child

But both were fairy-folk