adjective (a)

• feeling or expressing regret or sorrow or a sense of loss over something done or undone(adj.all)

  Example:
  Felt regretful over his vanished youth.
  Regretful over mistakes she had made.
  

  Synonym:
  bad, sorry
  Antonym:
  unregretful, unregretting
  

  source: wordnet30
• Full of regret; indulging in regrets; repining.(adjective)

  source: webster1913