Jethann is a prostitute in The Blooming Rose.
He is encountered during the quest The First Sacrifice. He was seeing Ninette de Carrac and is saddened to learn of her death.
After this first conversation, Hawke can sleep with him, regardless of the player's gender. If Hawke sleeps with him and Carver / Bethany or Aveline is in the party, then Carver / Bethany (+5) and Aveline (+5).
While his quest is active, it seems Hawke cannot interact with Madame Lusine to partner with any other prostitute on the premises. The only way to end this is if Hawke sleeps with Jethann or tells him about Ninette's death.