Who is Karl Richter from Up at the Villa and what is their importance?

Karl is the young fiddler playing at the restaurant where the princess hosts a party. While there, he chances to meet Mary and returns with her to her villa where they make love. Karl is a complicated character and is obviously overly-romantic and impoverished. He seems to be in a dire situation and it's this that apparently prompts his suicide after Mary tells him that they can never be together again.